Ultra-fine fibrous carbon for non-aqueous electrolyte secondary battery, ultra-fine fibrous carbon aggregate, composite, and electrode active material layer

ABSTRACT

The purpose of the present invention is to provide an electrode active material layer exhibiting excellent mechanical strength. This electrode material for a non-aqueous electrolyte secondary battery includes at least an electrode active material, a carbon-based conductive auxiliary agent, and a binder. The carbon-based conductive auxiliary agent has a linear structure, and includes ultra-fine fibrous carbon having an average fibre diameter of more than 200 nm but not more than 900 nm. The electrode material configures an electrode active material layer in which the maximum tensile strength (σ M ) in a planar direction and the tensile strength (σ T ) in an in-plane direction orthogonal to the maximum tensile strength (σ M ) satisfy relational expression (a), namely σ M /σ T ≦1.6.

TECHNICAL FIELD

The present invention relates to ultrafine fibrous carbons for anon-aqueous electrolyte secondary battery, particularly, for a lithiumion secondary battery, ultrafine-fibrous-carbon aggregates, and acomposite, and further relates to a carbon-based electroconductiveagent, an electrode active material layer, an electrode material, and anelectrode each using the same. In addition, the present inventionrelates to a non-aqueous secondary battery, particularly, a lithium ionsecondary battery, using the electrode.

BACKGROUND ART <Background Art of First and Second Aspects of thePresent Invention>

A lithium ion secondary battery as a kind of non-aqueous electrolytesecondary battery is a secondary battery where lithium ion in anelectrolyte is responsible for electrical conduction, and a secondarybattery using a lithium metal oxide for the positive electrode and acarbon material such as graphite for the negative electrode ispredominating. The lithium secondary battery is characterized by having,among secondary batteries, a high energy density and is expanding itsapplication range from small equipment such as cellular phone to largeequipment such as electric car.

One of the challenges for the lithium ion secondary battery is toprevent reduction (deterioration) in the battery capacity resulting fromrepetition of charging and discharging (enhancement of cyclecharacteristics). The cause of reduction in the cycle characteristics isconsidered to be, for example, a change (deterioration) of the electrodeactive material, electrolyte, electrolytic solution, etc., or anincrease in the electrode resistance due to separation between anelectrode foil and an electrode active material, and among others, onegreatest cause includes expansion/contraction of the active materialitself. As one improvement method therefor, it has been proposed toenhance the cycle characteristics by adding a fibrous carbon materialinto an electrode (see Patent Document 1).

In addition, since the carbon material added cannot sufficiently utilizeits characteristics when aggregated in the electrode, it has beenproposed to enhance the cycle characteristics by using a fibrous carbonmaterial improved in the dispersibility in an electrode (see PatentDocument 2).

<Background Art of Third and Fourth Aspects of the Present Invention>

As described in the background art of the first and second aspects ofthe present invention, one of the challenges for the lithium ionsecondary battery is to prevent reduction (deterioration) in the batterycapacity resulting from repetition of charging and discharging(enhancement of cycle characteristics).

For example, Patent Document 1 has proposed a negative electrode for alithium secondary battery, wherein the negative electrode for a lithiumsecondary battery contains a negative electrode active material capableof storing/releasing lithium, an electrically conductive carbon materialand a binder, the negative electrode active material is a graphiticmaterial using natural or artificial graphite in which the interplanarspacing d(002) of (002) plane of the graphite structure as measured bypowder X-ray diffraction is from 0.335 to 0.337 nm, the electricallyconductive carbon material is a vapor grown carbon fiber in which theaverage fiber diameter is from 1 to 200 nm and the fiber has a hollowstructure inside and has a structure of graphene sheets being laminatedin a direction perpendicular to the length direction of the fiber and inwhich the interplanar spacing d(002) of (002) plane of the graphitestructure as measured by powder X-ray diffraction is from 0.336 to 0.345nm, and the vapor grown carbon fiber is contained in an amount of 0.1 to10 mass % relative to the entire negative electrode without forming anagglomerate of 10 μm or more. In addition, for example, Patent Document3 has proposed a negative electrode active material ingredient for alithium secondary battery, containing at least either one graphitematerial of flake graphite or spherical graphite and a fibrous carbonforming a secondary particle having an average particle diameter of 10to 30 μm.

RELATED ART Patent Document

Patent Document 1: JP2007-42620A

Patent Document 2: JP2012-003985A

Patent Document 3: JP2000-133267A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention<Challenge for First Aspect of the Present Invention>

An object of the present invention is to provide an electrode activematerial layer excellent in mechanical strength, a non-aqueouselectrolyte secondary battery containing the electrode active materiallayer, and a carbon-based electroconductive agent contained in theelectrode active material layer. Another object of the present inventionis to provide a non-aqueous electrolyte secondary battery, particularly,a lithium ion secondary battery, with excellent cycle characteristics byincreasing the mechanical strength of an electrode active materiallayer.

<Challenge for Second Aspect of the Present Invention>

An object of the present invention is to provide a composite having highelectrical conductivity and excellent mechanical strength, acarbon-based electroconductive agent containing the composite, anelectrode material for a non-aqueous electrolyte secondary battery,containing the electroconductive agent, and an electrode for anon-aqueous electrolyte secondary battery, containing the electrodematerial. Another object of the present invention is to provide anon-aqueous electrolyte secondary battery, particularly, a lithium ionsecondary battery, with excellent rate characteristics by increasing theelectrical conductivity and mechanical strength of each of a composite,a carbon-based electroconductive agent containing the composite, anelectrode active material layer containing the composite, and anelectrode for a non-aqueous electrolyte secondary battery, containingthe electrode active material layer.

<Challenge for Third Aspect of the Present Invention>

In the invention described in Patent Document 1, a fibrous carbonmaterial is added in an electrode with an attempt to enhance the cyclecharacteristics, but since a vapor grown carbon fiber is used as thefibrous carbon material and the vapor grown carbon fiber has a branchingstructure, dispersibility in an electrode can be hardly increased andthe fibrous carbon material may aggregate, giving rise to a problem thatthe cycle characteristics are not sufficiently enhanced. The inventiondescribed in Patent Document 3 is characterized by adding from 0.5 to22.5 parts by mass of a vapor grown carbon fiber so as to contain, in anelectrode, a secondary particle composed of a vapor grown carbon fiberhaving an average particle diameter of 12 to 48 μm and thereby enhancethe cycle characteristics, but when a vapor grown carbon fiber islocalized, this is expected to allow focusing of a current on asecondary particle of the carbon fiber and intensively deteriorate onlythe focused portion, giving rise to a problem that the cyclecharacteristics are not sufficiently enhanced.

As a result of intensive studies by taking into account theabove-described problems, the present inventors have found that whenwater dispersibility of ultrafine fibrous carbons andultrafine-fibrous-carbon aggregates each for a non-aqueous electrolytesecondary battery is improved, the cycle characteristics of anon-aqueous electrolyte secondary battery, particularly, a lithium ionsecondary battery, can be enhanced and moreover, high capacity can beachieved.

An object of the present invention is to provide ultrafine fibrouscarbons and ultrafine-fibrous-carbon aggregates each having excellentwater dispersibility. Another object of the present invention is toprovide a carbon-based electroconductive agent, an electrode materialfor a non-aqueous electrolyte secondary battery, and an electrode for anon-aqueous electrolyte secondary battery, each having high electricalconductivity, by improving water dispersibility of ultrafine fibrouscarbons and/or ultrafine-fibrous-carbon aggregates. Still another objectof the present invention is to provide a non-aqueous electrolytesecondary battery, particularly, a lithium ion secondary battery, withexcellent cycle characteristics and high capacity by improving waterdispersibility of ultrafine fibrous carbons and/orultrafine-fibrous-carbon aggregates.

<Challenge for Fourth Aspect of the Present Invention>

As a result of intensive studies by taking into account the problemsdescribed in Challenge for Third Aspect of the Present Invention, thepresent inventors have found that when water dispersibility ofultrafine-fibrous-carbon aggregates for a non-aqueous electrolytesecondary battery is improved, the cycle characteristics of anon-aqueous electrolyte secondary battery, particularly, a lithium ionsecondary battery, can be enhanced and moreover, high capacity can beachieved.

An object of the present invention is to provideultrafine-fibrous-carbon aggregates having excellent waterdispersibility and excellent mechanical strength. Another object of thepresent invention is to provide a carbon-based electroconductive agent,an electrode material for a non-aqueous electrolyte secondary battery,and an electrode for a non-aqueous electrolyte secondary battery, eachhaving high electrical conductivity and excellent mechanical strength,by improving water dispersibility and mechanical strength ofultrafine-fibrous-carbon aggregates. Still another object of the presentinvention is to provide a non-aqueous electrolyte secondary battery,particularly, a lithium ion secondary battery, with excellent cyclecharacteristics and high capacity by improving water dispersibility andmechanical strength of ultrafine-fibrous-carbon aggregates.

Means to Solve the Problems <First Aspect of the Present Invention>

In order to attain the above-described objects, the present inventorshave repeated intensive studies by taking into account thoseconventional techniques, as a result, the present invention has beenaccomplished. That is, the present invention is an electrode activematerial layer containing at least an electrode active material, acarbon-based electroconductive agent and a binder, wherein thecarbon-based electroconductive agent contains ultrafine fibrous carbonshaving a linear structure and an average fiber diameter of more than 200nm to 900 nm and the in-plane maximum tensile strength σ_(M) of theelectrode active material layer and the in-plane tensile strength σ_(T)in the direction perpendicular to the direction of the maximum tensilestrength σ_(M) satisfy the following relationship (a):

σ_(M)/σ_(T≦)1.6  (a)

<Second Aspect of the Present Invention>

In order to attain the above-described objects, the present inventorshave repeated intensive studies by taking into account thoseconventional techniques, as a result, the present invention has beenaccomplished. That is, the present invention is a composite containingultrafine fibrous carbons and a spherical carbon, wherein the ultrafinefibrous carbons have a linear structure, and the ultrafine fibrouscarbons and the spherical carbon are integrally attached to each otherand uniformly mixed with each other.

<Third Aspect of the Present Invention>

In order to attain the above-described objects, the present inventionprovides ultrafine fibrous carbons having a linear structure, wherein atleast a part of the surface of the ultrafine fibrous carbons is modifiedwith a surfactant and/or at least a part of the surface of the ultrafinefibrous carbons is oxidatively treated, and also providesultrafine-fibrous-carbon aggregates obtained by aggregating theultrafine fibrous carbon.

<Fourth Aspect of the Present Invention>

In order to attain the above-described objects, the present inventionprovides ultrafine-fibrous-carbon aggregates obtained by aggregatingultrafine fibrous carbons having a linear structure, wherein at least apart of the surface of the ultrafine fibrous carbons in at least a partof the ultrafine-fibrous-carbon aggregates is modified with a surfactantand/or at least a part of the surface of the ultrafine fibrous carbonsin at least a part of the ultrafine-fibrous-carbon aggregates isoxidatively treated, and, in the volume-based particle size fiber lengthdistribution of the ultrafine-fibrous-carbon-aggregate, which isobtained by measuring the volume-based particle size distribution, afirst peak exists at a fiber length of 15 μm or less and a second peakexists at a fiber length of more than 15 μm, and the ratio of thevolume-based particle size distribution (%) of the first peak to thevolume-based particle size distribution (%) of the second peak is 3/1 ormore.

Effects of the Invention <Effects of First Aspect of the PresentInvention>

According to the present invention, an electrode active material layerexcellent in mechanical strength, a non-aqueous electrolyte secondarybattery containing the electrode active material layer, and acarbon-based electroconductive agent contained in the electrode activematerial layer are provided. In addition, according to the presentinvention, a non-aqueous electrolyte secondary battery, particularly, alithium ion secondary battery, with excellent cycle characteristics isprovided.

<Effects of Second Aspect of the Present Invention>

According to the present invention, a composite having high electricalconductivity and excellent mechanical strength, a carbon-basedelectroconductive agent containing the composite, an electrode activematerial layer containing the composite, and an electrode for anon-aqueous electrolyte secondary battery, containing the electrodeactive material layer, are provided. In addition, according to thepresent invention, a non-aqueous electrolyte secondary battery,particularly, a lithium ion secondary battery, having excellent cyclecharacteristics and high capacity is provided by increasing theelectrical conductivity and mechanical strength of each of a composite,a carbon-based electroconductive agent containing the composite, anelectrode active material layer containing the composite, and anelectrode for a non-aqueous electrolyte secondary battery, containingthe electrode active material layer.

<Effects of Third Aspect of the Present Invention>

According to the present invention, ultrafine fibrous carbons andultrafine-fibrous-carbon aggregates each having excellent waterdispersibility are provided. In addition, according to the presentinvention, a carbon-based electroconductive agent, an electrode materialfor a non-aqueous electrolyte secondary battery, and an electrode for anon-aqueous electrolyte secondary battery, each having high electricalconductivity are provided by improving water dispersibility of ultrafinefibrous carbons and/or ultrafine-fibrous-carbon aggregates. Furthermore,according to the present invention, a non-aqueous electrolyte secondarybattery, particularly, a lithium ion secondary battery, having excellentcycle characteristics and high capacity is provided by improving waterdispersibility of ultrafine fibrous carbons and/orultrafine-fibrous-carbon aggregates.

<Effects of Fourth Aspect of the Present Invention>

According to the present invention, ultrafine-fibrous-carbon aggregateshaving excellent water dispersibility and excellent mechanical strengthis provided. In addition, according to the present invention, acarbon-based electroconductive agent, an electrode material for anon-aqueous electrolyte secondary battery, and an electrode for anon-aqueous electrolyte secondary battery, each having high electricalconductivity and excellent mechanical strength, are provided byimproving water dispersibility and mechanical strength ofultrafine-fibrous-carbon aggregates. Furthermore, according to thepresent invention, a non-aqueous electrolyte secondary battery,particularly, a lithium ion secondary battery, having excellent cyclecharacteristics and high capacity is provided by improving waterdispersibility and mechanical strength of ultrafine-fibrous-carbonaggregates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscope image (2,000 timesmagnification) of ultrafine fibrous carbons.

FIG. 2 is a stress-strain curve showing the tensile test results of theelectrode active material layer for evaluation manufactured in ReferenceExample A1 (CNF).

FIG. 3 is a stress-strain curve showing the tensile test results of theelectrode active material layer for evaluation manufactured in ExampleA2 (S-CNF).

FIG. 4 is a stress-strain curve showing the tensile test results of theelectrode active material layer for evaluation manufactured in ExampleA3 (CNF/S-CNF).

FIG. 5 is a stress-strain curve showing the tensile test results of theelectrode active material layer for evaluation manufactured in ExampleA4 (CNF/AB).

FIG. 6 is a tress-strain curve showing the tensile test results of theelectrode active material layer for evaluation manufactured inComparative Example A1 (VGCF).

FIG. 7 is a stress-strain curve showing the tensile test results of theelectrode active material layer for evaluation manufactured inComparative Example A2 (AB).

FIG. 8 is a view showing the results of the stress (MPa) in the MDdirection (the coating direction for coating the electrode material(slurry) at the time of manufacture of the electrode) applied at 0.2%(0.1 mm) elongation of the electrode material layers manufactured inReference Example A1, Examples A2 to A4 and Comparative Examples A1 andA2.

FIG. 9 is a view showing the results of the stress (MPa) in the TDdirection (the in-plane direction perpendicular to the coating directionfor coating the electrode material (slurry) at the time of manufactureof the electrode) applied at 0.2% (0.1 mm) elongation of the electrodematerial layers manufactured in Reference Example A1, Examples A2 to A4and Comparative Examples A1 and A2.

FIG. 10 is a scanning electron microscope image (2,000 timesmagnification) of the ultrafine fibrous carbons used in ReferenceExample A1, Example A3 and Example A4 (CNF).

FIG. 11 is a scanning electron microscope image ((a) 2,000 times or (b)8,000 times magnification) of the ultrafine fibrous carbons used inExample A2 and Example A3 (S-CNF).

FIG. 12 is a scanning electron microscope image (8,000 timesmagnification) of acetylene black used in Example A4 (AB).

FIG. 13 is a scanning electron microscope image ((a) 5,000 times or (b)8,000 times magnification) of the electrode active material layermanufactured in Example A3 (CNF/S-CNF).

FIG. 14 is a scanning electron microscope image ((a) 5,000 times or (b)8,000 times magnification) of the electrode active material layermanufactured in Example A4 (CNF/AB).

FIG. 15 is a scanning electron microscope image (2,000 timesmagnification) of ultrafine fibrous carbons.

FIG. 16 is a scanning electron microscope image (2,000 timesmagnification) of the ultrafine fibrous carbons used in Example B1-1,Example B1-2 and Comparative Example B1-1 (CNF).

FIG. 17 is a photograph showing the observation results of a scanningelectron microscope image (500 times magnification) of Composite 1-1obtained in Example B1-1.

FIG. 18 is a photograph showing the observation results of a scanningelectron microscope image (1,000 times magnification) of Composite 1-1obtained in Example B1-1.

FIG. 19 is a photograph showing the observation results of a scanningelectron microscope image (500 times magnification) of Composite 1-2obtained in Example B1-2.

FIG. 20 is a photograph showing the observation results of a scanningelectron microscope image (1,000 times magnification) of Composite 1-2obtained in Example B1-2.

FIG. 21 is a view showing the results of the relationship between thedensity and the volume resistivity, obtained by performing Example B3and Comparative Example B2.

FIG. 22 is a chart of discharge rate characteristics of the cellmanufactured in Example B3-2 (CNF/AB).

FIG. 23 is a chart of discharge rate characteristics of the cellmanufactured in Example B3-3 (CNF/AB (ball mill)).

FIG. 24 is a chart of discharge rate characteristics of the cellmanufactured in Comparative Example B3-1 (CNF).

FIG. 25 is a chart of discharge rate characteristics of the cellmanufactured in Comparative Example B3-2 (AB).

FIG. 26 is a scanning electron microscope image (2,000 timesmagnification) of ultrafine fibrous carbons.

FIG. 27 is a scanning electron microscope image (2,000 timesmagnification) of the ultrafine fibrous carbons used in Example C1 andComparative Example C1 (CNF).

FIG. 28 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the slurry obtained in ExampleC1.

FIG. 29 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the slurry obtained in ExampleC2.

FIG. 30 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the slurry obtained in ExampleC3.

FIG. 31 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the slurry obtained inComparative Example C1.

FIG. 32 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the slurry obtained in ExampleC4.

FIG. 33 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the slurry obtained in ExampleC5.

FIG. 34 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the slurry obtained in ExampleC6.

FIG. 35 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the electrode obtained in ExampleC1.

FIG. 36 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the electrode obtained in ExampleC4.

FIG. 37 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the electrode obtained in ExampleC5.

FIG. 38 is a view showing the water dispersibility of theultrafine-fibrous-carbon aggregates in the electrode obtained in ExampleC6.

FIG. 39 is a scanning electron microscope image (2,000 timesmagnification) of ultrafine fibrous carbons.

FIG. 40 is a scanning electron microscope image (2,000 timesmagnification) of the ultrafine fibrous carbons used in Examples D1 andD2 and Comparative Examples D1 and D2 (CNF).

FIG. 41 is a view showing the results of the fiber length distributionof the ultrafine-fibrous-carbon aggregates obtained in Example D1.

FIG. 42 is a view showing the results of the fiber length distributionof the ultrafine-fibrous-carbon aggregates obtained in Example D2.

FIG. 43 is a view showing the results of the fiber length distributionof the ultrafine-fibrous-carbon aggregates obtained in ComparativeExample D1.

FIG. 44 is a view showing the results of the fiber length distributionof the ultrafine-fibrous-carbon aggregates obtained in ComparativeExample D2.

MODE FOR CARRYING OUT THE INVENTION <First Aspect of the PresentInvention>

The electrode active material layer according to the present inventioncontains at least an electrode active material, a carbon-basedelectroconductive agent and a binder, the carbon-based electroconductiveagent contains ultrafine fibrous carbons having a linear structure andan average fiber diameter of more than 200 nm to 900 nm, and thein-plane maximum tensile strength σ_(M) of the electrode active materiallayer and the in-plane tensile strength σ_(T) in the directionperpendicular to the direction of the maximum tensile strength σ_(M)satisfy the following relationship (a) (embodiment 1):

σ_(M)/σ_(T)≦1.6  (a)

According to embodiment 1, the maximum tensile strength σ_(M) and thetensile strength σ_(T) in the in-plane perpendicular direction areequivalent, and therefore even when the electrode active material isexpanded/contracted at the time of charging/discharging, cracking of theelectrode active material layer or separation of the electrode activematerial layer from the collector can be suppressed, so that the effectof excellent cycle characteristics can be provided.

In embodiment 1, the carbon-based electroconductive agent is preferablycontained in an amount of 10 mass % or less, based on the total mass ofthe electrode active material layer (embodiment 2). According toembodiment 2, the mechanical strength in the coating direction forcoating the electrode material (MD direction) and/or the in-planedirection perpendicular to the coating direction (TD direction) islarge, and an excellent reinforcement effect is provided.

In embodiment 1 or 2, the binder is preferably contained in an amount of1 to 25 mass %, based on the total mass of the electrode active materiallayer (embodiment 3). According to embodiment 3, the mechanical strengthin the coating direction for coating the electrode material (MDdirection) and/or the in-plane direction perpendicular to the coatingdirection (TD direction) is large, and an excellent reinforcement effectis provided.

In any one embodiment of embodiments 1 to 3, the average fiber length ofthe ultrafine fibrous carbons is preferably from 1 to 15 μm (embodiment4). According to embodiment 4, the mechanical strength in the coatingdirection for coating the electrode material (MD direction) and/or thein-plane direction perpendicular to the coating direction (TD direction)is large, and an excellent reinforcement effect is provided.

In any one embodiment of embodiments 1 to 4, the ultrafine fibrouscarbons preferably contains ultrafine fibrous carbons having an averagefiber length of 1 to 15 μm and ultrafine fibrous carbons having anaverage fiber length of more than 15 μm to 50 μm (embodiment 5).According to embodiment 5, the mechanical strength in the coatingdirection for coating the electrode material (MD direction) and/or thein-plane direction perpendicular to the coating direction (TD direction)is large, and an excellent reinforcement effect is provided.

In the electrode active material layer according to the presentinvention, two or more embodiments out of embodiments 1 to 5 can becombined.

In addition, the electrode active material layer according to thepresent invention preferably contains at least two kinds of ultrafinefibrous carbons differing in the average fiber length of the ultrafinefibrous carbon, and it is more preferred that the average fiber lengthof at least one kind of ultrafine fibrous carbons out of at least twokinds of ultrafine fibrous carbons is from 1 to 15 μm. Here, theultrafine fibrous carbons is sometimes referred to as CNF, and theultrafine fibrous carbons having a short average fiber length, forexample, ultrafine fibrous carbons having an average fiber length of 1to 15 μm, is sometimes referred to as S-CNF.

Furthermore, the electrode active material layer according to thepresent invention preferably contains ultrafine fibrous carbons and atleast one kind of a carbon-based material other than ultrafine fibrouscarbons, more preferably contains at least two kinds of ultrafinefibrous carbons differing in the average fiber length of the ultrafinefibrous carbons and at least one kind of a carbon-based material otherthan ultrafine fibrous carbons. The at least one kind of a carbon-basedmaterial other than ultrafine fibrous carbons includes, for example,carbon black, acetylene black, and graphite.

The non-aqueous electrolyte secondary battery according to the presentinvention is a non-aqueous electrolyte secondary battery containing theelectrode active material layer according to embodiments 1 to 5(embodiment 6). The electrode for the non-aqueous electrolyte secondarybattery using the electrode active material layer according toembodiments 1 to 5 can be increased in the mechanical strength, andtherefore even when the active material is expanded/contracted at thetime of charging/discharging, the non-aqueous electrolyte secondarybattery of embodiment 6 can maintain an electrical conduction path, sothat the effect of excellent cycle characteristics can be provided.

The carbon-based electroconductive agent according to the presentinvention contains ultrafine fibrous carbons having a linear structureand an average fiber diameter of more than 200 nm to 900 nm, and theaverage fiber length of the ultrafine fibrous carbons is from 1 to 15 μm(embodiment 7). Alternatively, the carbon-based electroconductive agentaccording to the present invention contains ultrafine fibrous carbonshaving a linear structure and an average fiber diameter of more than 200nm to 900 nm, and the ultrafine fibrous carbons contains ultrafinefibrous carbons having an average fiber length of 1 to 15 μm andultrafine fibrous carbons having an average fiber length of more than 15μm to 50 μm (embodiment 8). The electrode active material layercontaining the carbon-based electroconductive agent of embodiments 7 and8 has a large mechanical strength in the coating direction for coatingthe electrode material (MD direction) and the in-plane directionperpendicular to the coating direction (TD direction), and an excellentreinforcement effect is provided.

In addition, the carbon-based electroconductive agent according to thepresent invention preferably contains at least two kinds of ultrafinefibrous carbons differing in the average fiber length of the ultrafinefibrous carbon, and it is more preferred that the average fiber lengthof at least one kind of ultrafine fibrous carbons out of at least twokinds of ultrafine fibrous carbons is from 1 to 15 μm.

Furthermore, the electrode active material layer according to thepresent invention preferably contains ultrafine fibrous carbons and atleast one kind of a carbon-based material other than ultrafine fibrouscarbons, more preferably contains at least two kinds of ultrafinefibrous carbons differing in the average fiber length of the ultrafinefibrous carbons and at least one kind of a carbon-based material otherthan ultrafine fibrous carbons. The at least one kind of a carbon-basedmaterial other than ultrafine fibrous carbons includes, for example,carbon black, acetylene black, and graphite.

First, the ultrafine fibrous carbons contained in a carbon-basedelectroconductive agent that is contained in the electrode activematerial layer of the present invention, is described in detail.

Ultrafine Fibrous Carbon

Easily-Graphitizable Carbon

The ultrafine fibrous carbons contained in the electrode material for anon-aqueous electrolyte secondary battery according to the presentinvention is preferably easily-graphitizable carbon. Theeasily-graphitizable carbon is a raw carbon material in which a graphitestructure having a three-dimensional lamination regularity is readilyproduced by heat treatment at a high temperature of 2,500° C. or more,and is also called soft carbon, etc. The easily-graphitizable carbonincludes petroleum coke, coal pitch coke, polyvinyl chloride,3,5-dimethylphenolformaldehyde resin, etc.

Above all, a compound capable of forming an optically anisotropic phase(liquid crystal phase) in a molten state, which is called a mesophasepitch, or a mixture thereof is preferred, because high crystallinity andhigh electrical conductivity are expected. The mesophase pitch includes,for example, a petroleum-based mesophase pitch obtained from a petroleumresidue oil by a method based on hydrogenation and heat treatment or bya method based on hydrogenation, heat treatment and solvent extraction;a coal-based mesophase pitch obtained from a coal tar pitch by a methodbased on hydrogenation and heat treatment or by a method based onhydrogenation, heat treatment and solvent extraction; and a syntheticliquid crystal pitch obtained by polycondensation in the presence of asuper strong acid (e.g., HF, BF3) by using, as a raw material, anaromatic hydrocarbon such as naphthalene, alkylnaphthalene andanthracene. Among these, a synthetic liquid crystal pitch is preferredin view of not containing impurities.

Average Fiber Diameter

The average fiber diameter of the ultrafine fibrous carbons for use inthe present invention is from more than 200 nm to 900 nm. This averagefiber diameter is a value measured from a photographic view taken at amagnification of 2,000 times by a field emission scanning electronmicroscope. The average fiber diameter of the ultrafine fibrous carbonsis preferably from more than 230 nm to 600 nm, more preferably from morethan 250 nm to 500 nm, still more preferably from more than 250 nm to400 nm.

The ultrafine fibrous carbons for use in the present invention have alinear structure. The linear structure as used herein means that thebranching degree is 0.01 branch/μm or less. The branching indicates agranular part formed by bonding of ultrafine fibrous carbons to theother ultrafine fibrous carbons at a position other than the terminalpart, and indicates that the primary axis of the ultrafine fibrouscarbons is diverged in midstream and the primary axis of the ultrafinefibrous carbons has a branching secondary axis.

Average Fiber Length

The average fiber length of the ultrafine fibrous carbons for use in thepresent invention is preferably from 1 to 100 μm, more preferably from 1to 50 μm. As the average fiber length of the ultrafine fibrous carbonsis longer, the electrical conductivity in the electrode for anon-aqueous electrolyte secondary battery, the strength of theelectrode, and the electrolytic solution retentivity are advantageouslyincreased, but if it is too long, there arises a problem that the fiberdispersibility in the electrode is impaired. For this reason, theaverage fiber length of the ultrafine fibrous carbons for use in thepresent invention is preferably in the range above.

Average Interplanar Spacing

In the ultrafine fibrous carbons for use in the present invention, it ismore preferred that the average interplanar spacing d(002) of (002)plane as measured by an X-ray diffraction method is from 0.335 to 0.340nm.

Here, FIG. 1 shows a scanning electron micrograph (2,000 timesmagnification) of a representative ultrafine fibrous carbons for use inthe present invention. As evident from FIG. 1, it is confirmed that theultrafine fibrous carbons for use in the present invention has a linearstructure and the average fiber length is from 1 to 100 μm.

Next, the electrode active material (positive electrode active material,negative electrode active material) contained in the electrode materialfor a non-aqueous electrolyte secondary battery according to the presentinvention is described in detail.

[Positive Electrode Active Material]

As the positive electrode active material contained in the electrodematerial for a non-aqueous electrolyte secondary battery of the presentinvention, arbitrary one member or two or more members appropriatelyselected from the materials conventionally known as the positiveelectrode active material in a non-aqueous electrolyte secondary batterymay be used. For example, in the case of a lithium ion secondarybattery, a lithium-containing metal oxide capable of storing/releasinglithium ion is suitable. The lithium-containing metal oxide includes acomposite oxide containing lithium and at least one element selectedfrom the group consisting of Co, Mg, Mn, Ni, Fe, Al, Mo, V, W, Ti, etc.

Specifically, the composite oxide includes at least one member selectedfrom the group consisting of Li_(x)CoO₂, Li_(x)NiO₂, Li_(x)MnO₂,Li_(x)Co_(a)Ni_(1-a)O₂, Li_(x)Co_(b)V_(1-b)O_(z),Li_(x)Co_(b)Fe_(1-b)O₂, Li_(x)Mn₂O₄, Li_(x)Mn_(c)Co_(2-c)O₄,Li_(x)Mn_(c)Ni_(2-c)O₄, Li_(x)Mn_(c)V_(2-c)O₄, Li_(x)Mn_(c)Fe_(2-c)O₄(wherein x=from 0.02 to 1.2, a=from 0.1 to 0.9, b=from 0.8 to 0.98,c=from 1.6 to 1.96, and z=from 2.01 to 2.3), etc. Preferablelithium-containing metal oxides include at least one member selectedfrom the group consisting of Li_(x)CoO₂, Li_(x)NiO₂, Li_(x)MnO₂,Li_(x)Co_(a)Ni_(1-a)O₂, Li_(x)Mn₂O₄, and Li_(x)Co_(b)V_(1-b)O_(z) (wherex, a, b and z are the same as above). Incidentally, the value of x is avalue before start of charging/discharging and is increased/decreased bycharging/discharging.

As for the positive electrode active material above, one material may beused alone, or two or more materials may be used in combination. Theaverage particle diameter of the positive electrode active material is10 μm or less. If the average particle diameter exceeds 10 μm, theefficiency of charge/discharge reaction decreases under a large current.The average particle diameter is preferably from 0.05 μm (50 nm) to 7μm, more preferably from 1 to 7 μm.

[Negative Electrode Active Material]

As the negative electrode active material contained in the electrodematerial for a non-aqueous electrolyte secondary battery of the presentinvention, one member or two or more members selected from the materialsconventionally known as the negative electrode active material in anon-aqueous electrolyte secondary battery may be used. For example, inthe case of a lithium ion secondary battery, a carbon material capableof storing/releasing lithium ion, either Si or Sn, an alloy or oxidecontaining at least either one thereof, etc. may be used. Among these, acarbon material is preferred.

Representative examples of the carbon material include natural graphite,artificial graphite produced by heat-treating petroleum-based andcoal-based cokes, hard carbon in which a resin is carbonized, and amesophase pitch-based carbon material. In the case of using naturalgraphite or artificial graphite, from the standpoint of increasing thebattery capacity, those having a graphite structure in which theinterplanar spacing d(002) of (002) plane is from 0.335 to 0.337 nm asmeasured by powder X-ray diffraction are preferred.

The natural graphite means a graphitic material naturally produced as anore. The natural graphite is classified, by its appearance and nature,into two types, i.e., scaly graphite having a high degree ofcrystallization and amorphous graphite having a low degree ofcrystallization. The scaly graphite is further classified into flakygraphite taking on a leaf-like appearance and scaly graphite taking on ablock-like appearance. The natural graphite working out to a graphiticmaterial is not particularly limited in its locality, nature, and kind.In addition, natural graphite or a particle produced using naturalgraphite as a raw material may be heat-treated before use.

The artificial graphite means graphite produced by a wide range ofartificial techniques or a graphitic material close to a perfectgraphite crystal. Representative examples thereof include those producedthrough a calcination step at approximately from 500 to 1,000° C. and agraphitization step at 2,000° C. or more by using, as a raw material,tar or coke obtained from a residue, etc. after coal carbonization orcrude oil distillation. In addition, Kish graphite obtained byreprecipitating carbon from molten iron is also a kind of artificialgraphite.

Other than the carbon material, when an alloy containing at least eitherone of Si and Sn is used as the negative electrode active material, thisis effective in that the electric capacity can be reduced, compared witha case of using Si or Sn as an elemental substance or using an oxidethereof. Particularly an Si-based alloy is preferred.

The Si-based alloy includes, for example, an alloy of Si and at leastone element selected from the group consisting of B, Mg, Ca, Ti, Fe, Co,Mo, Cr, V, W, Ni, Mn, Zn, Cu, etc. Specifically, the alloy includes atleast one member selected from the group consisting of SiB₄, SiB₆,Mg₂Si, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu5Si, FeSi₂,MnSi₂, VSi₂, WSi₂, ZnSi₂, etc.

In the present invention, as the negative electrode active material, oneof the above-described materials may be used alone, or two or morethereof may be used in combination. The average particle diameter of thenegative electrode active material is 10 μm or less. If the averageparticle diameter exceeds 10 μm, the efficiency of charge/dischargereaction decreases under a large current. The average particle diameteris preferably from 0.1 to 10 μm, more preferably from 1 to 7 p.m.

The binder contained in the electrode material for a non-aqueouselectrolyte secondary battery of the present invention is described indetail below.

[Binder]

As for the binder contained in the non-aqueous electrolyte secondarybattery of the present invention, a binder enabling electrode moldingand having sufficient electrochemical stability can be suitably used. Assuch a binder, one or more members selected from the group consisting ofpolyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose,polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),synthetic butadiene rubber (SBR), a fluoroolefin copolymer crosslinkedpolymer, polyimide, petroleum pitch, coal pitch, a phenol resin, etc.are preferably used, and polyvinylidene fluoride (PVDF) is morepreferred.

The form at the time of use as a binder is not particularly limited andmay be a solid form or a liquid form (e.g., emulsion form), and the formcan be appropriately selected by taking into account, for example, theproduction method (in particular, whether dry kneading or wet kneading)of electrode and the solubility in electrolytic solution.

The solvent for dissolving the binder is not particularly limited aslong as it dissolves the binder. Specifically, the solvent includes, forexample, one or more kinds of solvents selected from the groupconsisting of N-methylpyrrolidone (NMP), dimethylacetamide (DMAc),dimethylformamide (DMF), dimethylsulfoxide (DMSO), etc. Particularly NMPor DMAc is preferred.

The electrode for a non-aqueous electrolyte secondary battery of thepresent invention is described below. The electrode for a non-aqueouselectrolyte secondary battery of the present invention is an electrodefor a non-aqueous electrolyte secondary battery, having a collector andan active material layer on the collector, wherein the active materiallayer is composed of the electrode material for a non-aqueouselectrolyte secondary battery of the present invention.

(Electrode for Non-Aqueous Electrolyte Secondary Battery)

As the method for manufacturing an electrode of a non-aqueouselectrolyte secondary battery, the following two techniques are employedin general. One method is a method where an electrode active material,an electroconductive agent and a binder are mixed/kneaded and shapedinto a film by extrusion molding, and the obtained film is rolled,stretched and then laminated together with a collector. Another methodis a method where an electrode active material, an electroconductiveagent, a binder and a solvent for dissolving the binder are mixed toprepare a slurry and the slurry is coated on a substrate and afterremoving the solvent, pressed.

In the present invention, either method may be used, but since thelatter method is preferred, the latter method is described in detailbelow.

In the manufacture of the electrode of the present invention, the ratioof the electroconductive agent added in the slurry is 10 mass % or lessrelative to the electrode material composed of the electrode activematerial, the electroconductive agent and the binder. The adding ratiois preferably 7 mass % or less, more preferably 5 mass % or less. If theratio of the electroconductive agent added exceeds 10 mass %, whenfabricating a cell having any capacity, the amount of the activematerial in the electrode is reduced, leading to difficulty ofapplication to power source usage where high importance is attached tothe energy density.

In the present invention, the ratio of the binder added is from 1 to 25mass % relative to the electrode material composed of the electrodeactive material, the electroconductive agent and the binder. The addingratio is preferably from 3 to 20 mass %, more preferably from 5 to 20mass %. If the amount of the binder is less than 1 mass %, generation ofcracking or separation of the electrode from the collector may occur. Ifthe amount of the binder exceeds 25 mass %, when fabricating a cellhaving any capacity, the amount of the active material in the electrodeis reduced, leading to difficulty of application to power source usagewhere high importance is attached to the energy density.

At the time of manufacture of the electrode, because of poor dispersionstate in the slurry, it is sometimes difficult to ensure fluiditysuitable for coating. In such a case, a slurrying aid may be used. Theslurrying aid includes, for example, one or more members selected fromthe group consisting of polyvinylpyrrolidone, carboxymethyl cellulose,polyvinyl acetate, polyvinyl alcohol, etc. Particularly use ofpolyvinylpyrrolidone is preferred. By adding the above-describedslurrying aid, sufficient fluidity can be ensured even with a relativelysmall amount of a solvent, and the dispersibility of pulverized activecarbon is also dramatically enhanced. In addition, generation ofcracking after the removal of solvent can be reduced. The amount of theslurrying aid added is preferably 10 mass % or less, more preferablyfrom 0.5 to 10 mass %, still more preferably from 0.5 to 8 mass %, basedon the total of components in the slurry other than the solvent. If theamount of the slurrying agent added exceeds 10 mass %, conversely, theslurry viscosity may decrease rapidly to cause a dispersion failure,making it difficult to manufacture a suitable slurry. If the value aboveis less than 0.5 mass %, the effect of the slurrying aid is not broughtout.

The solid content concentration in the slurry (the ratio of the totalweight of the slurry components other than the solvent to the total massof the slurry) is preferably from 10 to 50 mass %, more preferably from15 to 40 mass %. If the solid content concentration exceeds 50 mass %,it may be difficult to manufacture a uniform slurry. If this value isless than 10 mass %, the slurry viscosity may be decreased too much,resulting in uneven thickness of the electrode.

For coating the slurry, for example, an appropriate coating method suchas doctor blade may be employed. After the coating, the solvent isremoved by a treatment, for example, at 60 to 150° C., preferably from75 to 85° C., for preferably from 60 to 180 minutes. Thereafter, thecoated material after the removal of solvent is pressed, whereby anactive material layer can be produced.

In the electrode for a non-aqueous electrolyte secondary battery of thepresent invention, the thickness of the active material layer issuitably from 5 to 300 μm. If the thickness of the active material layeris less than 5 μm, when fabricating a cell having any capacity, aseparator or a collector needs to be used in a large amount, leading toa decrease in the volume occupancy of the active material layer in thecell, and not only this is disadvantageous in view of energy density butalso the usage is considerably limited. In particular, although outputcharacteristics (including low-temperature characteristics) areimportant, application to power source usage where high importance isattached to energy density becomes difficult.

On the other hand, production of an electrode where the electrodethickness exceeds 300 μm is relatively difficult due to problem of crackgeneration. Therefore, the electrode thickness is in general preferably300 μm or less in view of stable production of the electrode. In orderto more stably produce the electrode, the electrode thickness is morepreferably 200 μm or less and for the purpose of elevating theproductivity of electrode or the output characteristics of capacitor,the electrode thickness is still more preferably from 10 to 100 μm.

The electrode for a non-aqueous electrolyte secondary battery accordingto the present invention, which is manufactured as above, preferably hasno anisotropy of electrode strength. In the electrode having noanisotropy of electrode strength, from which the collector is removed,i.e., in the electrode material according to the present invention, theratio σ_(M)/σ_(T) between the tensile strength σ_(M) in the coatingdirection for coating the electrode material and the in-plane tensilestrength σ_(T) in the direction perpendicular to the direction of thecoating direction is preferably 1.6 or less. The ratio σ_(M)/σ_(T) ismore preferably 1.2 or less, still more preferably from 0.9 to 1.1.

The electrode for a non-aqueous electrolyte secondary battery accordingto the present invention, which is manufactured as above, preferably hasanisotropy of electrode strength. In the electrode having anisotropy ofelectrode strength, from which the collector is removed, i.e., in theelectrode material according to the present invention, the ratioσ_(M)/σ_(T) between the tensile strength σ_(M) in the coating directionfor coating the electrode material and the in-plane tensile strengthσ_(T) in the direction perpendicular to the direction of the coatingdirection is preferably more than 1.6. The ratio σ_(M)/σ_(T) is morepreferably 1.7 or more, still more preferably 1.8 or more.

The collector of the electrode for a non-aqueous electrolyte secondarybattery according to the present invention may be formed of anyelectrically conductive material. Accordingly, the collector can beformed of, for example, a metal material such as aluminum, nickel, iron,stainless steel, titanium and copper, particularly aluminum, stainlesssteel or copper.

The non-aqueous electrolyte secondary battery of the present inventionis described below. The non-aqueous electrolyte secondary battery of thepresent invention is a battery containing the electrode active materiallayer of the present invention.

(Non-Aqueous Electrolyte Secondary Battery)

The non-aqueous electrolyte secondary battery according to the presentinvention includes, for example, a lithium ion secondary battery, alithium battery, and a lithium ion polymer battery but is preferably alithium ion secondary battery. In the non-aqueous electrolyte secondarybattery of the present invention, a positive electrode obtained byforming a positive electrode active material layer on a surface of acollector, an electrolyte layer containing an electrolyte, and thenegative electrode for a non-aqueous electrolyte secondary battery ofthe present invention may be stacked such that the positive electrodematerial layer and the negative electrode active material layer of thenegative electrode according to the present invention face each otherand the electrolyte layer is inserted between the positive electrodeactive material layer and the negative electrode active material layeraccording to the present invention.

Alternatively, in the non-aqueous electrolyte secondary battery of thepresent invention, the positive electrode for a non-aqueous electrolytesecondary battery of the present invention, an electrolyte layercontaining an electrolyte, and a negative electrode obtained by forminga negative electrode active material layer on a surface of a collectormay be stacked such that the positive electrode active material layer ofthe positive electrode according to the present invention and thenegative electrode active material layer of the negative electrode faceeach other and the electrolyte layer is inserted between the positiveelectrode active material layer of the positive electrode according tothe present invention and the negative electrode active material layer.Furthermore, in the non-aqueous electrolyte secondary battery of thepresent invention, the positive electrode for a non-aqueous electrolytesecondary battery of the present invention, an electrolyte layercontaining an electrolyte, and the negative electrode for a non-aqueouselectrolyte secondary battery of the present invention may be stackedsuch that the positive electrode active material layer of the positiveelectrode according to the present invention and the negative electrodeactive material layer of the negative electrode according to the presentinvention face each other and the electrolyte layer is inserted betweenthe positive electrode active material layer of the positive electrodeaccording to the present invention and the negative electrode activematerial layer of the negative electrode according to the presentinvention.

The electrolyte layer for the non-aqueous electrolyte secondary batteryof the present invention is not limited as long as the object andeffects of the present invention are not impaired. Accordingly, as theelectrolyte layer, for example, a liquid electrolyte, i.e., a solutionprepared, for example, by dissolving a lithium salt in an organicsolvent, may be used. However, in the case of using such a liquidelectrolyte, a separator composed of a porous layer is preferably usedin general so as to prevent direct contact between the positiveelectrode active material layer and the negative electrode activematerial layer.

As the organic solvent for the liquid electrolyte, for example, ethylenecarbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC),dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) may be used.One of these organic solvents may be used alone, or two or more thereofmay be used in combination. As the lithium salt for the liquidelectrolyte, for example, LiPF₆, LiClO₄, LiN(CF₃SO₂)₂, and LiBF₄ can beused. One of these lithium salts may be used alone, or two or morethereof may be used in combination.

Incidentally, a solid electrolyte may also be used for the electrolytelayer and in this case, a separate spacer can be omitted.

(Carbon-Based Electroconductive Agent)

The carbon-based electroconductive agent according to the presentinvention contains ultrafine fibrous carbons having a linear structureand an average fiber diameter of more than 200 nm to 900 nm, and theaverage fiber length of the ultrafine fibrous carbons is from 1 to 15μm. Detailed description of the ultrafine fibrous carbons is as givenabove.

<Second Aspect of the Present Invention>

The present invention is described below.

The composite of the present invention is a composite containingultrafine fibrous carbons and a spherical carbon, wherein the ultrafinefibrous carbons has a linear structure and the ultrafine fibrous carbonsand the spherical carbon are integrally attached to each other anduniformly mixed with each other (embodiment 1).

In embodiment 1, the composite of the present invention is obtained bydry compounding of the ultrafine fibrous carbons and the sphericalcarbon (embodiment 2).

In embodiment 1 or 2, assuming that the density of the composite and thedensity of the ultrafine fibrous carbons are substantially identical,the composite of the present invention has a volume resistivity rangingfrom nearly the same as that of the ultrafine fibrous carbons to 1.5times (embodiment 3).

In any one embodiment of embodiments 1 to 3, assuming that the densityof the composite of the present invention and the density of thespherical carbon are substantially identical, the composite of thepresent invention has a volume resistivity ranging from nearly the sameas that of the spherical carbon to 1/100 times (embodiment 4).

In the composite according to any one embodiment of embodiments 1 to 4,the mass ratio between the ultrafine fibrous carbons and the sphericalcarbon is from 1:9 to 5:5 (embodiment 5).

In the composite according to any one embodiment of embodiments 1 to 5,the average fiber length of the ultrafine fibrous carbons is from morethan 10 μm to 50 μm (embodiment 6).

In the composite according to any one embodiment of embodiments 1 to 5,the average fiber length of the ultrafine fibrous carbons is from 1 to10 μm (embodiment 7).

In the composite according to any one embodiment of embodiments 1 to 7,the spherical carbon is carbon black (embodiment 8).

The carbon-based electroconductive agent of the present invention is acarbon-based electroconductive agent containing the composite accordingto any one embodiment of embodiments 1 to 7 (embodiment 9).

The electrode active material layer of the present invention is theelectrode active material layer according to any one embodiment ofembodiments 1 to 5 in the first aspect of the present invention,containing at least the composite according to embodiments 1 to 8, anelectrode active material, and a binder (embodiment 10).

The non-aqueous electrolyte secondary battery of the present inventionis a non-aqueous electrolyte secondary battery containing the electrodeactive material layer of embodiment 10 (embodiment 11).

In the composite of the present invention, two or more embodiments outof embodiments 1 to 8 can be arbitrarily combined. The carbon-basedelectroconductive agent of the present invention can contain thecomposite of the present invention in which two or more embodiments arearbitrarily combined; the electrode active material of the presentinvention can contain this composite; the electrode for a non-aqueouselectrolyte secondary battery of the present invention can contain thiselectrode active material layer; and the non-aqueous electrolytesecondary battery of the present invention can contain this electrodefor a non-aqueous electrolyte secondary battery.

The present invention is described in more detail below.

[Composite]

The composite of the present invention is a composite containingultrafine fibrous carbons and a spherical carbon, wherein the ultrafinefibrous carbons has a linear structure and the ultrafine fibrous carbonsand the spherical carbon are integrally attached to each other anduniformly mixed with each other. Due to the configuration where theultrafine fibrous carbons and the spherical carbon are integrallyattached to each other and uniformly mixed with each other, thecomposite of the present invention has high electrical conductivity andexcellent mechanical strength.

The “attached” as used herein may be chemical bonding but mainly meansphysical bonding, for example, means physical boding such as adhesion.Whether or not those carbons are integrally attached to each other anduniformly mixed can be easily judged by observing the mixing degree ofultrafine fibrous carbons and spherical carbon contained in thecomposite by means of a scanning electron microscope, etc. Whether ornot those carbons are integrally attached to each other and uniformlymixed can also be judged by measuring the porosity of the composite. Forjudging that the carbons are uniformly mixed, the porosity of thecomposite can be selected from, for example, 50% or less, 40% or less,and 30% or less, and may be 10% or more.

In order to achieve the configuration where ultrafine fibrous carbonsand a spherical carbon in the composite of the present invention areintegrally attached to each other and uniformly mixed with each other,the composite of the present invention is preferably produced andobtained by dry compounding or wet compounding of the superfine fibrouscarbon and the spherical carbon.

In particular, the composite of the present invention is more preferablyproduced by dry compounding of the superfine fibrous carbon and thespherical carbon. By applying dry compounding, the composite of thepresent invention can have both high electrical conductivity andexcellent mechanical strength. Dry compounding means that the superfinefibrous carbon and the spherical carbon are pulverized, dispersed andthereby compounded by means of a dry mill, etc.

Wet compounding means that the superfine fibrous carbon and thespherical carbon are pulverized, dispersed, and thereby compounded in anorganic solvent, etc. by means of a wet mill, etc.

Assuming that the density of the composite of the present invention andthe density of the ultrafine fibrous carbons are substantiallyidentical, the composite of the present invention preferably has avolume resistivity ranging from nearly the same as that of the ultrafinefibrous carbons to 50 times, and more preferably has a volumeresistivity of 30 times or less, still more preferably 10 times or less.The volume resistivity (unit: Ω·cm) as used herein means the resistanceper unit area and is used as a measure of electrical conductivity. Thatis, a lower value of the volume resistivity (unit: Ω·cm) indicatesbetter electrical conductivity.

Assuming that the density of the composite of the present invention andthe density of the spherical carbon are substantially identical, thecomposite of the present invention preferably has a volume resistivityranging from nearly the same as that of the spherical carbon to 1/100times.

In composite of the present invention, the mass ratio between theultrafine fibrous carbons and the spherical carbon is preferably from1:9 to 5:5. In the composite of the present invention, when the massratio of the ultrafine fibrous carbons is decreased, the volumeresistivity of the composite of the present invention approaches thevolume resistivity of the spherical carbon, and therefore the mass ratiobetween the ultrafine fibrous carbons and the spherical carbon is morepreferably from 4:6 to 5:5, still more preferably 5:5.

The ultrafine fibrous carbons contained in the composite of the presentinvention is not particularly limited as long as the object of thepresent invention is achieved and furthermore, the effects of thepresent invention are produced, but the ultrafine fibrous carbons ispreferably easily-graphitizable carbon. The easily-graphitizable carbonis a raw carbon material in which a graphite structure having athree-dimensional lamination regularity is readily produced by heattreatment at a high temperature of 2,500° C. or more, and is also calledsoft carbon, etc. The easily-graphitizable carbon includes petroleumcoke, coal pitch coke, polyvinyl chloride,3,5-dimethylphenolformaldehyde resin, etc.

Above all, a compound capable of forming an optically anisotropic phase(liquid crystal phase) in a molten state, which is called a mesophasepitch, or a mixture thereof is preferred, because high crystallinity andhigh electrical conductivity are expected. The mesophase pitch includes,for example, a petroleum-based mesophase pitch obtained from a petroleumresidue oil by a method based on hydrogenation and heat treatment or bya method based on hydrogenation, heat treatment and solvent extraction;a coal-based mesophase pitch obtained from a coal tar pitch by a methodbased on hydrogenation and heat treatment or by a method based onhydrogenation, heat treatment and solvent extraction; and a syntheticliquid crystal pitch obtained by polycondensation in the presence of asuper strong acid (e.g., HF, BF3) by using, as a raw material, anaromatic hydrocarbon such as naphthalene, alkylnaphthalene andanthracene. Among these, a synthetic liquid crystal pitch is preferredin view of not containing impurities.

(Average Fiber Diameter)

The average fiber diameter of the ultrafine fibrous carbons for use inthe present invention is from more than 200 nm to 900 nm. This averagefiber diameter is a value measured from a photographic view taken at amagnification of 2,000 times by a field emission scanning electronmicroscope. The average fiber diameter of the ultrafine fibrous carbonsis preferably from more than 230 nm to 600 nm, more preferably from morethan 250 nm to 500 nm, still more preferably from more than 250 nm to400 nm.

The ultrafine fibrous carbons for use in the present invention have alinear structure. The linear structure as used herein means that thebranching degree is 0.01 branch/μm or less. The branching indicates agranular part formed by bonding of ultrafine fibrous carbons to anotherultrafine fibrous carbons at a position other than the terminal part andindicates that the primary axis of the ultrafine fibrous carbons isdiverged in midstream and the primary axis of the ultrafine fibrouscarbons has a branching secondary axis.

(Average Fiber Length)

The average fiber length of the ultrafine fibrous carbons for use in thepresent invention may be from 1 to 100 μm. In the composite of thepresent invention, in view of electrical conductivity, mechanicalstrength and dispersibility, the average fiber length of the ultrafinefibrous carbons is preferably from more than 10 μm to 50 μm or from 1 to10 μm. This is because, if the average fiber length of the ultrafinefibrous carbons for use in the present invention exceeds 100 μm,dispersibility of the ultrafine fibrous carbons may be impaired. In thedescription of the present invention, the ultrafine fibrous carbons issometimes referred to as CNF, and the ultrafine fibrous carbons having ashort average fiber length, for example, ultrafine fibrous carbonshaving an average fiber length of 1 to 15 μm, is sometimes referred toas S-CNF.

(Average Interplanar Spacing)

In the ultrafine fibrous carbons for use in the present invention, it ismore preferred that the average interplanar spacing d(002) of (002)plane as measured by an X-ray diffraction method is from 0.335 to 0.340nm.

Here, FIG. 15 shows a scanning electron micrograph (2,000 timesmagnification) of a representative ultrafine fibrous carbons for use inthe present invention. As evident from FIG. 15, it is confirmed that theultrafine fibrous carbons for use in the present invention has a linearstructure and the average fiber length is from 1 to 100 μm.

The ultrafine fibrous carbons (CNF or S-CNF) for use in the presentinvention is produced by a known production method. For example, theultrafine fibrous carbons (CNF or S-CNF) can be produced by theproduction method described in JP2010-13742A or JP2010-31439A.

The spherical carbon for use in the present invention is preferablycarbon black. The carbon black includes, for example, acetylene black,furnace black, channel black, and thermal black and is preferablyacetylene black.

[Electroconductive Agent]

The carbon-based electroconductive agent of the present invention is acarbon-based electroconductive agent containing the composite of thepresent invention. The carbon-based electroconductive agent of thepresent invention contains the composite of the present invention andmay further contain a material other than the composite of the presentinvention, for example, a carbon-based material, as long as theelectrical conductivity of the electrode active material can beenhanced.

[Electrode Active Material Layer]

The electrode active material layer of the present invention is composedof the later-described electrode material for a non-aqueous electrolytesecondary battery.

The electrode material for a non-aqueous electrolyte secondary battery,which is used for forming the electrode active material layer of thepresent invention, is an electrode material for a non-aqueouselectrolyte secondary battery, containing at least the carbon-basedelectroconductive agent of the present invention, an electrode activematerial, and a binder.

The electrode active material (positive electrode active material,negative electrode active material) contained in the electrode materialfor a non-aqueous electrolyte secondary battery according to the presentinvention is described below.

(Positive Electrode Active Material)

As the positive electrode active material contained in the electrodematerial for a non-aqueous electrolyte secondary battery of the presentinvention, any one member or two or more members appropriately selectedfrom the materials conventionally known as the positive electrode activematerial in a non-aqueous electrolyte secondary battery may be used. Forexample, in the case of a lithium ion secondary battery, alithium-containing metal oxide capable of storing/releasing lithium ionis suitable. The lithium-containing metal oxide includes a compositeoxide containing lithium and at least one element selected from thegroup consisting of Co, Mg, Mn, Ni, Fe, Al, Mo, V, W, Ti, etc.

Specifically, the composite oxide includes at least one member selectedfrom the group consisting of Li_(x)CoO₂, Li_(x)NiO₂, Li_(x)MnO₂,Li_(x)Co_(a)Ni_(1-a)O₂, Li_(x)Co_(b)V_(1-b)O_(z),Li_(x)Co_(b)Fe_(1-b)O₂, Li_(x)Mn₂O₄, Li_(x)Mn_(c)Co_(2-c)O₄,Li_(x)Mn_(c)Ni_(2-c)O₄, Li_(x)Mn_(c)V_(2-c)O₄, Li_(x)Mn_(c)Fe_(2-c)O₄(wherein x=from 0.02 to 1.2, a=from 0.1 to 0.9, b=from 0.8 to 0.98,c=from 1.6 to 1.96, and z=from 2.01 to 2.3), etc. Preferablelithium-containing metal oxides include at least one member selectedfrom the group consisting of Li_(x)CoO₂, Li_(x)NiO₂, Li_(x)MnO₂,Li_(x)Co_(a)Ni_(1-a)O₂, Li_(x)Mn₂O₄, and Li_(x)Co_(b)V_(1-b)O_(z) (wherex, a, b and z are the same as above). Incidentally, the value of x is avalue before start of charging/discharging and is increased/decreased bycharging/discharging.

As for the positive electrode active material above, one material may beused alone, or two or more materials may be used in combination. Theaverage particle diameter of the positive electrode active material is10 μm or less. If the average particle diameter exceeds 10 μm, theefficiency of charge/discharge reaction decreases under a large current.The average particle diameter is preferably from 0.05 μm (50 nm) to 7μm, more preferably from 1 to 7 μm.

(Negative Electrode Active Material)

As the negative electrode active material contained in the electrodematerial for a non-aqueous electrolyte secondary battery of the presentinvention, one member or two or more members selected from the materialsconventionally known as the negative electrode active material in anon-aqueous electrolyte secondary battery may be used. For example, inthe case of a lithium ion secondary battery, a carbon material capableof storing/releasing lithium ion, either Si or Sn, an alloy or oxidecontaining at least either one thereof, etc. may be used. Among these, acarbon material is preferred.

Representative examples of the carbon material include natural graphite,artificial graphite produced by heat-treating petroleum-based andcoal-based cokes, hard carbon in which a resin is carbonized, and amesophase pitch-based carbon material. In the case of using naturalgraphite or artificial graphite, from the standpoint of increasing thebattery capacity, those having a graphite structure in which theinterplanar spacing d(002) of (002) plane is from 0.335 to 0.337 nm asmeasured by powder X-ray diffraction are preferred.

The natural graphite means a graphitic material naturally produced as anore. The natural graphite is classified, by its appearance and nature,into two types, i.e., scaly graphite having a high degree ofcrystallization and amorphous graphite having a low degree ofcrystallization. The scaly graphite is further classified into flakygraphite taking on a leaf-like appearance and scaly graphite taking on ablock-like appearance. The natural graphite working out to a graphiticmaterial is not particularly limited in its locality, nature, and kind.In addition, natural graphite or a particle produced using naturalgraphite as a raw material may be heat-treated before use.

The artificial graphite means graphite produced by a wide range ofartificial techniques or a graphitic material close to a perfectgraphite crystal. Representative examples thereof include those producedthrough a calcination step at approximately from 500 to 1,000° C. and agraphitization step at 2,000° C. or more by using, as a raw material,tar or coke obtained from a residue, etc. after coal carbonization orcrude oil distillation. In addition, Kish graphite obtained byreprecipitating carbon from molten iron is also a kind of artificialgraphite.

Other than the carbon material, when an alloy containing at least eitherone of Si and Sn is used as the negative electrode active material, thisis effective in that the electric capacity can be reduced, compared witha case of using Si or Sn as an elemental substance or using an oxidethereof. Particularly an Si-based alloy is preferred.

The Si-based alloy includes, for example, an alloy of Si and at leastone element selected from the group consisting of B, Mg, Ca, Ti, Fe, Co,Mo, Cr, V, W, Ni, Mn, Zn, Cu, etc. Specifically, the alloy includes atleast one member selected from the group consisting of SiB₄, SiB₆,Mg₂Si, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu₅Si, FeSi₂,MnSi₂, VSi₂, WSi₂, ZnSi₂, etc.

In the present invention, as the negative electrode active material, oneof the above-described materials may be used alone, or two or morethereof may be used in combination. The average particle diameter of thenegative electrode active material is 10 μm or less. If the averageparticle diameter exceeds 10 μm, the efficiency of charge/dischargereaction decreases under a large current. The average particle diameteris preferably from 0.1 to 10 μm, more preferably from 1 to 7 μm.

(Binder)

As for the binder contained in the non-aqueous electrolyte secondarybattery of the present invention, a binder enabling electrode moldingand having sufficient electrochemical stability can be suitably used. Assuch a binder, one or more members selected from the group consisting ofpolyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose,polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),synthetic butadiene rubber (SBR), a fluoroolefin copolymer crosslinkedpolymer, polyimide, petroleum pitch, coal pitch, a phenol resin, etc.are preferably used, and polyvinylidene fluoride (PVDF) is morepreferred.

The form at the time of use as a binder is not particularly limited andmay be a solid form or a liquid form (e.g., emulsion form), and the formcan be appropriately selected by taking into account, for example, theproduction method (in particular, whether dry kneading or wet kneading)of electrode and the solubility in electrolytic solution.

The solvent for dissolving the binder is not particularly limited aslong as it dissolves the binder. Specifically, the solvent includes, forexample, one or more kinds of solvents selected from the groupconsisting of N-methylpyrrolidone (NMP), dimethylacetamide (DMAc),dimethylformamide (DMF), dimethylsulfoxide (DMSO), etc. Particularly NMPor DMAc is preferred.

[Electrode for Non-Aqueous Electrolyte Secondary Battery]

The electrode for a non-aqueous electrolyte secondary battery of thepresent invention is an electrode for a non-aqueous electrolytesecondary battery, having a collector and an active material layer onthe collector, wherein the active material layer is composed of theelectrode material for a non-aqueous electrolyte secondary battery ofthe present invention.

As the method for manufacturing an electrode of a non-aqueouselectrolyte secondary battery, the following two techniques are employedin general. One method is a method where an electrode active material,an electroconductive agent and a binder are mixed/kneaded and shapedinto a film by extrusion molding and the film is rolled, stretched andthen laminated together with a collector. Another method is a methodwhere an electrode active material, an electroconductive agent, a binderand a solvent for dissolving the binder are mixed to prepare a slurryand the slurry is coated on a substrate and after removing the solvent,pressed.

In the present invention, either method may be used, but since thelatter method is preferred, the latter method is described in detailbelow.

In the manufacture of the electrode of the present invention, the ratioof the electroconductive agent added in the slurry is 10 mass % or lessrelative to the electrode material composed of the electrode activematerial, the electroconductive agent and the binder. The adding ratiois preferably 7 mass % or less, more preferably 5 mass % or less. If theratio of the electroconductive agent added exceeds 10 mass %, whenfabricating a cell having any capacity, the amount of the activematerial in the electrode is reduced, leading to difficulty ofapplication to power source usage where high importance is attached tothe energy density.

In the present invention, the ratio of the binder added is from 1 to 25mass % relative to the electrode material composed of the electrodeactive material, the electroconductive agent and the binder. The addingratio is preferably from 3 to 20 mass %, more preferably from 5 to 20mass %. If the amount of the binder is less than 1 mass %, generation ofcracking or separation of the electrode from the collector may occur. Ifthe amount of the binder exceeds 25 mass %, when fabricating a cellhaving any capacity, the amount of the active material in the electrodeis reduced, leading to difficulty of application to power source usagewhere high importance is attached to the energy density.

At the time of manufacture of the electrode, because of poor dispersionstate in the slurry, it is sometimes difficult to ensure fluiditysuitable for coating. In such a case, a slurrying aid may be used. Theslurrying aid includes, for example, one or more members selected fromthe group consisting of polyvinylpyrrolidone, carboxymethyl cellulose,polyvinyl acetate, polyvinyl alcohol, etc. Particularly use ofpolyvinylpyrrolidone is preferred. By adding the above-describedslurrying aid, sufficient fluidity can be ensured even with a relativelysmall amount of a solvent, and the dispersibility of pulverized activecarbon is also dramatically enhanced. In addition, generation ofcracking after the removal of solvent can be reduced. The amount of theslurrying aid added is preferably 10 mass % or less, more preferablyfrom 0.5 to 10 mass %, still more preferably from 0.5 to 8 mass %, basedon the total of components in the slurry other than the solvent. If theamount of the slurrying agent added exceeds 10 mass %, conversely, theslurry viscosity may decrease rapidly to cause a dispersion failure,making it difficult to manufacture a suitable slurry. If the value aboveis less than 0.5 mass %, the effect of the slurrying aid is not broughtout.

The solid content concentration in the slurry (the ratio of the totalweight of the slurry components other than the solvent to the total massof the slurry) is preferably from 10 to 50 mass %, more preferably from15 to 40 mass %. If the solid content concentration exceeds 50 mass %,it may be difficult to manufacture a uniform slurry. If this value isless than 10 mass %, the slurry viscosity may be decreased too much,resulting in uneven thickness of the electrode.

For coating the slurry, for example, an appropriate coating method suchas doctor blade may be employed. After the coating, the solvent isremoved by a treatment, for example, at 60 to 150° C., preferably from75 to 85° C., for preferably from 60 to 180 minutes. Thereafter, thecoated material after the removal of solvent is pressed, whereby anactive material layer can be produced.

In the electrode for a non-aqueous electrolyte secondary battery of thepresent invention, the thickness of the active material layer issuitably from 5 to 300 μm. If the thickness of the active material layeris less than 5 μm, when fabricating a cell having any capacity, aseparator or a collector needs to be used in a large amount, leading toa decrease in the volume occupancy of the active material layer in thecell, and not only this is disadvantageous in view of energy density butalso the usage is considerably limited. In particular, although outputcharacteristics (including low-temperature characteristics) areimportant, application to power source usage where high importance isattached to energy density becomes difficult.

On the other hand, production of an electrode where the electrodethickness exceeds 300 μm is relatively difficult due to problem of crackgeneration. Therefore, the electrode thickness is in general preferably300 μm or less in view of stable production of the electrode. In orderto more stably produce the electrode, the electrode thickness is morepreferably 200 μm or less and for the purpose of elevating theproductivity of electrode or the output characteristics of capacitor,the electrode thickness is still more preferably from 10 to 100 μm.

The electrode for a non-aqueous electrolyte secondary battery accordingto the present invention, which is manufactured as above, preferably hasno anisotropy of electrode strength. In the electrode having noanisotropy of electrode strength, from which the collector is removed,i.e., in the electrode material according to the present invention, theratio μM/σT between the tensile strength σM in the coating direction forcoating the electrode material and the in-plane tensile strength σ_(T)in the direction perpendicular to the direction of the coating directionis preferably 1.6 or less. The ratio σM/σT is more preferably 1.2 orless, still more preferably from 0.9 to 1.1.

The electrode for a non-aqueous electrolyte secondary battery accordingto the present invention, which is manufactured as above, preferably hasanisotropy of electrode strength. In the electrode having anisotropy ofelectrode strength, from which the collector is removed, i.e., in theelectrode material according to the present invention, the ratio σM/σTbetween the tensile strength σM in the coating direction for coating theelectrode material and the in-plane tensile strength σ_(T) in thedirection perpendicular to the direction of the coating direction ispreferably more than 1.6. The ratio σM/σT is more preferably 1.7 ormore, still more preferably 1.8 or more.

The collector of the electrode for a non-aqueous electrolyte secondarybattery according to the present invention may be formed of anyelectrically conductive material. Accordingly, the collector can beformed of, for example, a metal material such as aluminum, nickel, iron,stainless steel, titanium and copper, particularly aluminum, stainlesssteel or copper.

[Non-Aqueous Electrolyte Secondary Battery]

The non-aqueous electrolyte secondary battery of the present inventionis a non-aqueous secondary battery containing the electrode for anon-aqueous electrolyte secondary battery of the present invention.

The non-aqueous electrolyte secondary battery according to the presentinvention includes, for example, a lithium ion secondary battery, alithium battery, and a lithium ion polymer battery but is preferably alithium ion secondary battery. In the non-aqueous electrolyte secondarybattery of the present invention, a positive electrode obtained byforming a positive electrode material layer on a surface of a collector,an electrolyte layer containing an electrolyte, and the negativeelectrode for a non-aqueous electrolyte secondary battery of the presentinvention may be stacked such that the positive electrode material layerand the negative electrode material layer of the negative electrodeaccording to the present invention face each other and the electrolytelayer is inserted between the positive electrode material layer and thenegative electrode material layer according to the present invention.

Alternatively, in the non-aqueous electrolyte secondary battery of thepresent invention, the positive electrode for a non-aqueous electrolytesecondary battery of the present invention, an electrolyte layercontaining an electrolyte, and a negative electrode obtained by forminga negative electrode material layer on a surface of a collector may bestacked such that the positive electrode material layer of the positiveelectrode according to the present invention and the negative electrodematerial layer of the negative electrode face each other and theelectrolyte layer is inserted between the positive electrode materiallayer of the positive electrode according to the present invention andthe negative electrode material layer of the negative electrode.Furthermore, in the non-aqueous electrolyte secondary battery of thepresent invention, the positive electrode for a non-aqueous electrolytesecondary battery of the present invention, an electrolyte layercontaining an electrolyte, and the negative electrode for a non-aqueouselectrolyte secondary battery of the present invention may be stackedsuch that the positive electrode material layer of the positiveelectrode according to the present invention and the negative electrodematerial layer of the negative electrode according to the presentinvention face each other and the electrolyte layer is inserted betweenthe positive electrode material layer of the positive electrodeaccording to the present invention and the negative electrode materiallayer of the negative electrode according to the present invention.

The electrolyte layer for the non-aqueous electrolyte secondary batteryof the present invention is not limited as long as the object andeffects of the present invention are not impaired. Accordingly, as theelectrolyte layer, for example, a liquid electrolyte, i.e., a solutionprepared, for example, by dissolving a lithium salt in an organicsolvent, may be used. However, in the case of using such a liquidelectrolyte, a separator composed of a porous layer is preferably usedin general so as to prevent direct contact between the positiveelectrode active material layer and the negative electrode activematerial layer.

As the organic solvent for the liquid electrolyte, for example, ethylenecarbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC),dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) may be used.One of these organic solvents may be used alone, or two or more thereofmay be used in combination. As the lithium salt for the liquidelectrolyte, for example, LiPF₆, LiClO₄, LiN(CF₃SO₂)₂, and LiBF₄ can beused. One of these lithium salts may be used alone, or two or morethereof may be used in combination.

Incidentally, a solid electrolyte may also be used for the electrolytelayer and in this case, a separate spacer can be omitted.

<Third Aspect of the Present Invention>

The present invention is described below.

The ultrafine fibrous carbons of the present invention is ultrafinefibrous carbons having a linear structure, wherein at least a part ofthe surface of the ultrafine fibrous carbons is modified with asurfactant and/or at least a part of the surface of the ultrafinefibrous carbons is oxidatively treated (embodiment 1). The ultrafinefibrous carbons of the present invention has excellent waterdispersibility due to a configuration where at least a part of thesurface of the ultrafine fibrous carbons is modified with a surfactant,at least a part of the surface of the ultrafine fibrous carbons isoxidatively treated, or at least a part of the surface of the ultrafinefibrous carbons is modified with a surfactant and oxidatively treated.

In embodiment 1, the ultrafine fibrous carbons of the present inventionis ultrafine fibrous carbons that is disintegrated (embodiment 2).According to embodiment 2, the ultrafine fibrous carbons of the presentinvention is disintegrated, whereby the water dispersibility of theultrafine fibrous carbons is more enhanced.

In embodiment 2, the ultrafine fibrous carbons of the present inventionis ultrafine fibrous carbons that is disintegrated by a dry pulverizerand/or a wet pulverizer (embodiment 3). According to embodiment 3, theultrafine fibrous carbons of the present invention is disintegrated by adry pulverizer and/or a wet pulverizer, whereby the water dispersibilityof the ultrafine fibrous carbons is more enhanced.

In any one embodiment of embodiments 1 to 3, the ultrafine fibrouscarbons of the present invention is ultrafine fibrous carbons where theaspect ratio is from 1 to 1,000 (embodiment 4).

The ultrafine-fibrous-carbon aggregates of the present invention isultrafine-fibrous-carbon aggregates obtained by aggregating theultrafine fibrous carbons according to any one embodiment of embodiments1 to 4 (embodiment 5). According to embodiment 5, theultrafine-fibrous-carbon aggregates of the present invention hasexcellent water dispersibility.

The carbon-based electroconductive agent of the present invention is acarbon-based electroconductive agent containing the ultrafine fibrouscarbons according to any one embodiment of embodiments 1 to 4 and/or theultrafine-fibrous-carbon aggregates according to embodiment 5(embodiment 6). According to embodiment 6, the carbon-basedelectroconductive agent of the present invention has excellentelectrical conductivity, i.e., high electrical conductivity.

The electrode material for a non-aqueous electrolyte secondary batteryof the present invention is an electrode material for a non-aqueouselectrolyte secondary battery, containing at least the carbon-basedelectroconductive agent according to embodiment 6, an electrode activematerial, and a binder (embodiment 7). According to embodiment 7, theelectrode material for a non-aqueous electrolyte secondary battery ofthe present invention has high electrical conductivity.

In embodiment 7, the electrode material for a non-aqueous electrolytesecondary battery of the present invention is an electrode material fora non-aqueous electrolyte secondary battery, which further containswater as a solvent (embodiment 8). According to embodiment 8, the waterdispersibility of the ultrafine fibrous carbons and/orultrafine-fibrous-carbon aggregates is further improved, and theelectrode material for a non-aqueous electrolyte secondary battery ofthe present invention has higher electrical conductivity.

The electrode for a non-aqueous electrolyte secondary battery of thepresent invention is an electrode for a non-aqueous electrolytesecondary battery, having a collector and an active material layer onthe collector, wherein the active material layer is composed of theelectrode material for a non-aqueous electrolyte secondary batteryaccording to embodiment 7 or 8 (embodiment 9). According to embodiment9, the electrode for a non-aqueous electrolyte secondary battery of thepresent invention has high electrical conductivity.

The non-aqueous electrolyte secondary battery of the present inventionis a non-aqueous electrolyte secondary battery containing the electrodefor a non-aqueous electrolyte secondary battery according to embodiment9 (embodiment 10). The water dispersibility of the ultrafine fibrouscarbons and/or ultrafine-fibrous-carbon aggregates is improved, wherebythe non-aqueous electrolyte secondary battery of the present inventionhas excellent cycle characteristics and high capacity.

The ultrafine fibrous carbons of the present invention may be ultrafinefibrous carbons where at least two embodiments out of embodiments 1 to 4are arbitrarily combined. The ultrafine-fibrous-carbon aggregates of thepresent invention may be ultrafine-fibrous-carbon aggregates obtained byaggregating ultrafine fibrous carbons where at least two embodiments outof embodiments 1 to 4 are arbitrarily combined. The carbon-basedelectroconductive agent of the present invention may contain thisultrafine fibrous carbons and/or ultrafine-fibrous-carbon aggregate, theelectrode material for a non-aqueous electrolyte secondary battery ofthe present invention may contain this carbon electroconductive agent,the electrode for a non-aqueous electrolyte secondary battery of thepresent invention may contain this electrode material for a non-aqueouselectrolyte secondary battery, and the non-aqueous electrolyte secondarybattery of the present invention may contain this electrode for anon-aqueous electrolyte secondary battery.

The present invention is described in more detail below.

[Ultrafine Fibrous Carbon]

The ultrafine fibrous carbons of the present invention is ultrafinefibrous carbons having a linear structure, wherein at least a part ofthe surface of the ultrafine fibrous carbons is modified with asurfactant and/or at least a part of the surface of the ultrafinefibrous carbons is oxidatively treated. The linear structure as usedherein means that the branching degree is 0.01 branch/μm or less. Thebranching indicates a granular part formed by bonding of ultrafinefibrous carbons to another ultrafine fibrous carbons at a position otherthan the terminal part and indicates that the primary axis of theultrafine fibrous carbons is diverged in midstream and the primary axisof the ultrafine fibrous carbons has a branching secondary axis.

The ultrafine fibrous carbons of the present invention has excellentwater dispersibility due to a configuration where a part or the entiretyof the surface of the ultrafine fibrous carbons is modified with asurfactant. In addition, the ultrafine fibrous carbons of the presentinvention has excellent water dispersibility due to a configurationwhere a part or the entirety of the surface of the ultrafine fibrouscarbons is oxidatively treated. A part of the surface of the ultrafinefibrous carbons includes, for example, the surface at an edge of theultrafine fibrous carbon. The water dispersibility means the degree ofdispersion, i.e., dispersibility, of the ultrafine fibrous carbons in anaqueous solution or water (e.g., ion-exchanged water).

Modifying at least a part of the surface of the ultrafine fibrouscarbons with a surfactant means to cause chemical modification, physicalmodification, or chemical modification and further physicalmodification, between the ultrafine fibrous carbons and a surfactant.Chemical modification means that the ultrafine fibrous carbons and asurfactant undergo a chemical reaction and are thereby chemicallybonded, and means, for example, that a functional group of the ultrafinefibrous carbons and a functional group of the surfactant are covalentlybonded. Physical modification means not chemical bonding but physicalbonding and means, for example, that a surfactant is adsorbed or adheredto the ultrafine fibrous carbon.

The surfactant for modifying the ultrafine fibrous carbons of thepresent invention includes, for example, an anionic surfactant (e.g.,sodium carboxymethyl cellulose (CMC-Na), sodium fatty acid, sodiumalkylbenzenesulfonate), an cationic surfactant (e.g.,alkyltrimethylammonium salt, dialkyldimethylammonium salt), anamphoteric surfactant (e.g., alkyldimethylamine oxide,alkylcarboxybetaine), and a nonionic surfactant (e.g., polyoxyethylenealkyl ether, fatty acid diethanolamide), with sodium carboxymethylcellulose (CMC-Na) being preferred.

The mass ratio between the ultrafine fibrous carbons and the surfactantfor modifying the ultrafine fibrous carbons is not particularly limitedas long as the object of the present invention is achieved andfurthermore, the effects of the present invention are produced, but themass ratio is preferably 5:6.

The method for modifying at least a part of the surface of theultrafine-fibrous-carbon fibers with a surfactant is not particularlylimited, but preferable methods include a method of mixing theultrafine-fibrous-carbon fibers and a surfactant in an“electrode-forming solution”, and a method where the ultrafine fibrouscarbons is dispersed in an organic solvent allowing for gooddispersibility of the ultrafine fibrous carbon, a surfactant or asolution having dissolved therein a surfactant is added to the solutionobtained above, and the solvent is then removed by heating, etc.Particularly the latter method is more preferred, because a surfactantcan modify the ultrafine fibrous carbons in a dispersed state, andtherefore surfactant-modified ultrafine-fibrous-carbon fibers that isless likely to cause agglomeration of the ultrafine fibrous carbons atthe time of manufacture of the electrode is obtained.

The organic solvent allowing for good dispersibility of theultrafine-fibrous-carbon fibers is not particularly limited as long asthe ultrafine-fibrous-carbon fibers is successfully dispersed, but theorganic solvent includes an organic solvent having high affinity for acarbon material. The organic solvent having high affinity for a carbonmaterial includes alcohols, esters, amides, ethers, etc., and in view ofhigh affinity, amides are preferred.

In the case of removing the solvent after the modification with asurfactant, the organic solvent allowing for good dispersibility of theultrafine-fibrous-carbon fibers is preferably less volatile than thesolvent for dissolving the surfactant, because at the time of heatingand concentrating the solvent, the organic solvent allowing for gooddispersibility of the ultrafine-fibrous-carbon fibers can be kept at ahigh concentration and the dispersibility of theultrafine-fibrous-carbon fibers can be maintained.

The solvent for dissolving the surfactant is not particularly limited aslong as it is a solvent capable of dissolving the surfactant and havingcompatibility with the “organic solvent allowing for good dispersibilityof the ultrafine-fibrous-carbon fibers”, but preferred examples thereofinclude an alcohol and water.

In the case where the solvent for dissolving the surfactant is water,for example, NMP or pyridine is preferably used as the organic solventallowing for good dispersibility of the ultrafine-fibrous-carbon fibers,because at the time of heating and concentrating the solvent, theorganic solvent allowing for good dispersibility of theultrafine-fibrous-carbon fibers can be kept at a high concentration andthe dispersibility of the ultrafine-fibrous-carbon fibers can bemaintained.

Specific examples of the oxidative treatment applied to at least a partof the surface of the ultrafine fibrous carbons include an oxidativetreatment with peroxide (H₂O₂), an oxidative treatment with ozone, anoxidative treatment by UV irradiation, an oxidative treatment in air,and an oxidative treatment with an acid such as mixed acid. From thestandpoint that an ionic carboxyl group is produced on the surface ofthe ultrafine fibrous carbons of the present invention by an oxidativetreatment with peroxide (H₂O₂) and the crystal structure of theultrafine fibrous carbons is less damaged, an oxidative treatment withperoxide (H₂O₂) is preferred.

In view of enhancing water dispersibility, the ultrafine fibrous carbonsof the present invention is preferably ultrafine fibrous carbons that isdisintegrated, more preferably ultrafine fibrous carbons that isdisintegrated by a dry pulverizer and/or a wet pulverizer, still morepreferably ultrafine fibrous carbons that is disintegrated by a dry jetmill as one example of the dry pulverizer and/or a wet jet mill as oneexample of the wet pulverizer, because more improvement of the waterdispersibility can be achieved. Furthermore, the ultrafine fibrouscarbons of the present invention may be ultrafine fibrous carbons thatis pulverized by a dry mill or a wet mill. The pulverization means thatthe ultrafine fibrous carbons is disintegrated and crushed (shorteningof length of the ultrafine fibrous carbon).

The ultrafine fibrous carbons of the present invention is preferablyultrafine fibrous carbons where the aspect ratio is from 1 to 1,000,more preferably ultrafine fibrous carbons where the aspect ratio is from5 to 500, still more preferably ultrafine fibrous carbons where theaspect ratio is from 10 to 100.

The ultrafine fibrous carbons of the present invention is notparticularly limited as long as the object of the present invention isachieved and furthermore, the effects of the present invention areproduced, but the ultrafine fibrous carbons is preferablyeasily-graphitizable carbon. The easily-graphitizable carbon is a rawcarbon material in which a graphite structure having a three-dimensionallamination regularity is readily produced by heat treatment at a hightemperature of 2,500° C. or more, and is also called soft carbon, etc.The easily-graphitizable carbon includes petroleum coke, coal pitchcoke, polyvinyl chloride, 3,5-dimethylphenolformaldehyde resin, etc.

Above all, a compound capable of forming an optically anisotropic phase(liquid crystal phase) in a molten state, which is called a mesophasepitch, or a mixture thereof is preferred, because high crystallinity andhigh electrical conductivity are expected. The mesophase pitch includes,for example, a petroleum-based mesophase pitch obtained from a petroleumresidue oil by a method based on hydrogenation and heat treatment or bya method based on hydrogenation, heat treatment and solvent extraction;a coal-based mesophase pitch obtained from a coal tar pitch by a methodbased on hydrogenation and heat treatment or by a method based onhydrogenation, heat treatment and solvent extraction; and a syntheticliquid crystal pitch obtained by polycondensation in the presence of asuper strong acid (e.g., HF, BF₃) by using, as a raw material, anaromatic hydrocarbon such as naphthalene, alkylnaphthalene andanthracene. Among these, a synthetic liquid crystal pitch is preferredin view of not containing impurities.

(Average Fiber Diameter)

The average fiber diameter of the ultrafine fibrous carbons of thepresent invention is preferably from more than 200 nm to 900 nm. Thisaverage fiber diameter is a value measured from a photographic viewtaken at a magnification of 2,000 times by a field emission scanningelectron microscope. The average fiber diameter of the ultrafine fibrouscarbons is more preferably from more than 230 nm to 600 nm, still morepreferably from more than 250 nm to 500 nm, yet still more preferablyfrom more than 250 nm to 400 nm.

(Average Fiber Length)

The average fiber length of the ultrafine fibrous carbons of the presentinvention is preferably from 1 to 100 μm. In the ultrafine fibrouscarbons of the present invention, in view of water dispersibility andelectrical conductivity, the average fiber length of the ultrafinefibrous carbons is preferably from more than 10 μm to 50 μm or from 1 to10 μm. In addition, ultrafine fibrous carbons having an average fiberlength of 1 to 10 μm and ultrafine fibrous carbons having an averagefiber length of more than 10 μm to 50 μm may be contained in any ratioin the ultrafine-fibrous-carbon aggregates of the present invention.Because if the average fiber length of the ultrafine fibrous carbons ofthe present invention exceeds 100 μm, water dispersibility of theultrafine fibrous carbons or ultrafine-fibrous-carbon aggregates may beimpaired. In the description of the present invention, the ultrafinefibrous carbons is sometimes referred to as CNF, and the ultrafinefibrous carbons having a short average fiber length, for example,ultrafine fibrous carbons having an average fiber length of 1 to 10 μm,is sometimes referred to as S-CNF.

(Average Interplanar Spacing)

The average interplanar spacing of the ultrafine fibrous carbons for usein the present invention is not particularly limited as long as theobject of the present invention is achieved and furthermore, the effectsof the present invention are produced, but the average interplanarspacing d(002) of (002) plane as measured by an X-ray diffraction methodis preferably from 0.335 to 0.340 nm.

Here, FIG. 26 shows a scanning electron micrograph (2,000 timesmagnification) of a representative ultrafine fibrous carbons of thepresent invention. As evident from FIG. 26, it is confirmed that theultrafine fibrous carbons for use in the present invention has a linearstructure and the average fiber length is from 1 to 100 μm.

The ultrafine fibrous carbons (CNF or S-CNF) of the present invention isproduced by a known production method. For example, the ultrafinefibrous carbons (CNF or S-CNF) can be produced by the production methoddescribed in JP2010-13742A, JP2010-31439A, etc.

[Ultrafine-Fibrous-Carbon Aggregates]

The ultrafine-fibrous-carbon aggregates of the present invention areultrafine-fibrous-carbon aggregates obtained by aggregating theultrafine fibrous carbons of the present invention. Theultrafine-fibrous-carbon aggregates of the present invention arecomposed by aggregation of the ultrafine fibrous carbons of the presentinvention, and therefore have excellent water dispersibility.

[Electroconductive Agent]

The carbon-based electroconductive agent of the present invention is acarbon-based electroconductive agent containing the ultrafine fibrouscarbons and/or ultrafine-fibrous-carbon aggregates of the presentinvention. The carbon-based electroconductive agent of the presentinvention has excellent electrical conductivity, i.e., high electricalconductivity, by virtue of containing the ultrafine fibrous carbonsand/or ultrafine-fibrous-carbon aggregates of the present invention. Thecarbon-based electroconductive agent of the present invention containsthe ultrafine fibrous carbons and/or ultrafine-fibrous-carbon aggregatesof the present invention and as long as the electrical conductivity canbe enhanced, may further contain a material other than the ultrafinefibrous carbons and/or ultrafine-fibrous-carbon aggregates of thepresent invention, for example, a carbon-based material.

[Electrode Material for Non-Aqueous Electrolyte Secondary Battery]

The electrode material for a non-aqueous electrolyte secondary batteryof the present invention is an electrode material for a non-aqueouselectrolyte secondary battery, containing at least the carbon-basedelectroconductive agent of the present invention, an electrode activematerial, and a binder. The electrode material for a non-aqueouselectrolyte secondary battery of the present invention has excellentelectrical conductivity, i.e., high electrical conductivity, by virtueof containing the carbon-based electroconductive agent of the presentinvention.

The electrode material for a non-aqueous electrolyte secondary batteryof the present invention preferably further contains water as a solvent.Water as the solvent includes, for example, ion-exchanged water. Byfurther containing water as a solvent, the water dispersibility of theultrafine fibrous carbons and/or ultrafine-fibrous-carbon aggregates ofthe present invention is more improved, and the electrode material for anon-aqueous electrolyte secondary battery of the present invention hashigher electrical conductivity.

The electrode active material (positive electrode active material,negative electrode active material) contained in the electrode materialfor a non-aqueous electrolyte secondary battery of the present inventionis described below.

(Positive Electrode Active Material)

As the positive electrode active material contained in the electrodematerial for a non-aqueous electrolyte secondary battery of the presentinvention, any one member or two or more members appropriately selectedfrom the materials conventionally known as the positive electrode activematerial in a non-aqueous electrolyte secondary battery may be used. Forexample, in the case of a lithium ion secondary battery, alithium-containing metal oxide capable of storing/releasing lithium ionis suitable. The lithium-containing metal oxide includes a compositeoxide containing lithium and at least one element selected from thegroup consisting of Co, Mg, Mn, Ni, Fe, Al, Mo, V, W, Ti, etc.

Specifically, the composite oxide includes at least one member selectedfrom the group consisting of Li_(x)CoO₂, Li_(x)NiO₂, Li_(x)MnO₂,Li_(x)Co_(a)Ni_(1-a)O₂, Li_(x)Co_(b)V_(1-b)O_(z),Li_(x)Co_(b)Fe_(1-b)O₂, Li_(x)Mn₂O₄, Li_(x)Mn_(c)Co_(2-c)O₄,Li_(x)Mn_(c)Ni_(2-c)O₄, Li_(x)Mn_(c)V_(2-c)O₄, Li_(x)Mn_(c)Fe_(2-c)O₄(wherein x=from 0.02 to 1.2, a=from 0.1 to 0.9, b=from 0.8 to 0.98,c=from 1.6 to 1.96, and z=from 2.01 to 2.3), etc. Preferablelithium-containing metal oxides include at least one member selectedfrom the group consisting of Li_(x)CoO₂, Li_(x)NiO₂, Li_(x)MnO₂,Li_(x)Co_(a)Ni_(1-a)O₂, Li_(x)Mn₂O₄, and Li_(x)Co_(b)V_(1-b)O_(z) (wherex, a, b and z are the same as above). Incidentally, the value of x is avalue before start of charging/discharging and is increased/decreased bycharging/discharging.

As for the positive electrode active material above, one material may beused alone, or two or more materials may be used in combination. Theaverage particle diameter of the positive electrode active material is10 μm or less. If the average particle diameter exceeds 10 μm, theefficiency of charge/discharge reaction decreases under a large current.The average particle diameter is preferably from 0.05 μm (50 nm) to 7μm, more preferably from 1 to 7 μm.

(Negative Electrode Active Material)

As the negative electrode active material contained in the electrodematerial for a non-aqueous electrolyte secondary battery of the presentinvention, one member or two or more members selected from the materialsconventionally known as the negative electrode active material in anon-aqueous electrolyte secondary battery may be used. For example, inthe case of a lithium ion secondary battery, a carbon material capableof storing/releasing lithium ion, either Si or Sn, an alloy or oxidecontaining at least either one thereof, etc. may be used. Among these, acarbon material is preferred.

Representative examples of the carbon material include natural graphite,artificial graphite produced by heat-treating petroleum-based andcoal-based cokes, hard carbon in which a resin is carbonized, and amesophase pitch-based carbon material. In the case of using naturalgraphite or artificial graphite, from the standpoint of increasing thebattery capacity, those having a graphite structure in which theinterplanar spacing d(002) of (002) plane is from 0.335 to 0.337 nm asmeasured by powder X-ray diffraction are preferred.

The natural graphite means a graphitic material naturally produced as anore. The natural graphite is classified, by its appearance and nature,into two types, i.e., scaly graphite having a high degree ofcrystallization and amorphous graphite having a low degree ofcrystallization. The scaly graphite is further classified into flakygraphite taking on a leaf-like appearance and scaly graphite taking on ablock-like appearance. The natural graphite working out to a graphiticmaterial is not particularly limited in its locality, nature, and kind.In addition, natural graphite or a particle produced using naturalgraphite as a raw material may be heat-treated before use.

The artificial graphite means graphite produced by a wide range ofartificial techniques or a graphitic material close to a perfectgraphite crystal. Representative examples thereof include those producedthrough a calcination step at approximately from 500 to 1,000° C. and agraphitization step at 2,000° C. or more by using, as a raw material,tar or coke obtained from a residue, etc. after coal carbonization orcrude oil distillation. In addition, Kish graphite obtained byreprecipitating carbon from molten iron is also a kind of artificialgraphite.

Other than the carbon material, when an alloy containing at least eitherone of Si and Sn is used as the negative electrode active material, thisis effective in that the electric capacity can be reduced, compared witha case of using Si or Sn as an elemental substance or using an oxidethereof. Particularly an Si-based alloy is preferred.

The Si-based alloy includes, for example, an alloy of Si and at leastone element selected from the group consisting of B, Mg, Ca, Ti, Fe, Co,Mo, Cr, V, W, Ni, Mn, Zn, Cu, etc. Specifically, the alloy includes atleast one member selected from the group consisting of SiB₄, SiB₆,Mg₂Si, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu₅Si, FeSi₂,MnSi₂, VSi₂, WSi₂, ZnSi₂, etc.

In the present invention, as the negative electrode active material, oneof the above-described materials may be used alone, or two or morethereof may be used in combination. The average particle diameter of thenegative electrode active material is 10 μm or less. If the averageparticle diameter exceeds 10 μm, the efficiency of charge/dischargereaction under a large current decreases. The average particle diameteris preferably from 0.1 to 10 μm, more preferably from 1 to 7 μm.

(Binder)

As for the binder contained in the non-aqueous electrolyte secondarybattery of the present invention, a binder enabling electrode moldingand having sufficient electrochemical stability can be suitably used. Assuch a binder, one or more members selected from the group consisting ofpolyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose,polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),synthetic butadiene rubber (SBR), a fluoroolefin copolymer crosslinkedpolymer, polyimide, petroleum pitch, coal pitch, a phenol resin, etc.are preferably used, and polyvinylidene fluoride (PVDF) is morepreferred.

The form at the time of use as a binder is not particularly limited andmay be a solid form or a liquid form (e.g., emulsion form), and the formcan be appropriately selected by taking into account, for example, theproduction method (in particular, whether dry kneading or wet kneading)of electrode and the solubility in electrolytic solution.

The solvent for dissolving the binder is not particularly limited aslong as it dissolves the binder. Specifically, the solvent includes, forexample, one or more kinds of solvents selected from the groupconsisting of N-methylpyrrolidone (NMP), dimethylacetamide (DMAc),dimethylformamide (DMF), dimethylsulfoxide (DMSO), etc. Particularly NMPor DMAc is preferred.

[Electrode for Non-Aqueous Electrolyte Secondary Battery]

The electrode for a non-aqueous electrolyte secondary battery of thepresent invention is an electrode for a non-aqueous electrolytesecondary battery, having a collector and an active material layer onthe collector, wherein the active material layer is composed of theelectrode material for a non-aqueous electrolyte secondary battery ofthe present invention. The electrode for a non-aqueous electrolytesecondary battery of the present invention is a positive electrode whenhaving a positive electrode active material layer on the collector, andis a negative electrode when having a negative electrode active materiallayer on the collector. The electrode for a non-aqueous electrolytesecondary battery of the present invention has excellent electricalconductivity, i.e., high electrical conductivity, and excellentmechanical strength by virtue of containing, as an active materiallayer, the electrode material for a non-aqueous electrolyte secondarybattery of the present invention. The ultrafine fibrous carbons andultrafine-fibrous-carbon aggregates of the present invention haveexcellent water dispersibility, and therefore the electrode material fora non-aqueous electrolyte secondary battery of the present invention iseasily formed into a paste when slurried, so that the electrode for anon-aqueous electrolyte secondary battery of the present invention canbe easily produced.

As the method for manufacturing the electrode of a non-aqueouselectrolyte secondary battery of the present invention, the followingtwo techniques are employed in general. One method is a method where anelectrode active material, an electroconductive agent and a binder aremixed/kneaded and shaped into a film by extrusion molding and the filmis rolled, stretched and then laminated together with a collector.Another method is a method where an electrode active material, anelectroconductive agent, a binder and a solvent for dissolving thebinder are mixed to prepare a slurry and the slurry is coated on asubstrate and after removing the solvent, pressed.

In the present invention, either method may be used, but since thelatter method is preferred, the latter method is described in detailbelow.

In the manufacture of the electrode for a non-aqueous electrolytesecondary battery of the present invention, the ratio of theelectroconductive agent of the present invention added in the slurry is10 mass % or less relative to the electrode material for a non-aqueouselectrolyte secondary battery of the present invention, which iscomposed of the electrode active material, the electroconductive agentand the binder. The adding ratio is preferably 7 mass % or less, morepreferably 5 mass % or less. If the ratio of the electroconductive agentadded exceeds 10 mass %, when fabricating a cell having any capacity,the amount of the active material in the electrode is reduced, leadingto difficulty of application to power source usage where high importanceis attached to the energy density.

In the present invention, the ratio of the binder added is from 1 to 25mass % relative to the electrode material composed of the electrodeactive material, the electroconductive agent and the binder. The addingratio is preferably from 3 to 20 mass %, more preferably from 5 to 20mass %. If the amount of the binder is less than 1 mass %, generation ofcracking or separation of the electrode from the collector may occur. Ifthe amount of the binder exceeds 25 mass %, when fabricating a cellhaving any capacity, the amount of the active material in the electrodeis reduced, leading to difficulty of application to power source usagewhere high importance is attached to the energy density.

At the time of manufacture of the electrode, because of poor dispersionstate in the slurry, it is sometimes difficult to ensure fluiditysuitable for coating. In such a case, a slurrying aid may be used. Theslurrying aid includes, for example, one or more members selected fromthe group consisting of polyvinylpyrrolidone, carboxymethyl cellulose,polyvinyl acetate, polyvinyl alcohol, etc. Particularly use ofpolyvinylpyrrolidone is preferred. By adding the above-describedslurrying aid, sufficient fluidity can be ensured even with a relativelysmall amount of a solvent, and the dispersibility of pulverized activecarbon is also dramatically enhanced. In addition, generation ofcracking after the removal of solvent can be reduced.

The solid content concentration in the slurry (the ratio of the totalweight of the slurry components other than the solvent to the total massof the slurry) is preferably from 10 to 50 mass %, more preferably from15 to 40 mass %. If the solid content concentration exceeds 50 mass %,it may be difficult to manufacture a uniform slurry. If this value isless than 10 mass %, the slurry viscosity may be decreased too much,resulting in uneven thickness of the electrode.

For coating the slurry, for example, an appropriate coating method suchas doctor blade may be employed. After the coating, the solvent isremoved by a treatment, for example, at 60 to 150° C., preferably from75 to 85° C., for preferably from 60 to 180 minutes. Thereafter, thecoated material after the removal of solvent is pressed, whereby anactive material layer can be produced.

In the electrode for a non-aqueous electrolyte secondary battery of thepresent invention, the thickness of the active material layer issuitably from 5 to 300 μm. If the thickness of the active material layeris less than 5 μm, when fabricating a cell having any capacity, aseparator or a collector needs to be used in a large amount, leading toa decrease in the volume occupancy of the active material layer in thecell, and not only this is disadvantageous in view of energy density butalso the usage is considerably limited. In particular, although outputcharacteristics (including low-temperature characteristics) areimportant, application to power source usage where high importance isattached to energy density becomes difficult.

On the other hand, production of an electrode where the electrodethickness exceeds 300 μm is relatively difficult due to problem of crackgeneration. Therefore, the electrode thickness is in general preferably300 μm or less in view of stable production of the electrode. In orderto more stably produce the electrode, the electrode thickness is morepreferably 200 μm or less and for the purpose of elevating theproductivity of electrode or the output characteristics of capacitor,the electrode thickness is still more preferably from 10 to 100 μm.

The electrode for a non-aqueous electrolyte secondary battery of thepresent invention, which is manufactured as above, preferably has noanisotropy of mechanical strength (electrode strength) in view ofreinforcement effect. In the electrode having no anisotropy ofmechanical strength (electrode strength), from which the collector isremoved, i.e., in the electrode material for a non-aqueous electrolytesecondary battery of the present invention, the ratio σM/σT between thetensile strength σM in the coating direction for coating the electrodematerial and the in-plane tensile strength σ_(T) in the directionperpendicular to the direction of the coating direction is preferably1.6 or less. The ratio σM/σT is more preferably 1.2 or less, still morepreferably from 0.9 to 1.1.

The electrode for a non-aqueous electrolyte secondary battery of thepresent invention, which is manufactured as above, preferably hasanisotropy of mechanical strength (electrode strength) in view ofreinforcement effect. In the electrode having anisotropy of mechanicalstrength (electrode strength), from which the collector is removed,i.e., in the electrode material for a non-aqueous electrolyte secondarybattery of the present invention, the ratio σM/σT between the tensilestrength σM in the coating direction for coating the electrode materialand the in-plane tensile strength σ_(T) in the direction perpendicularto the direction of the coating direction is preferably more than 1.6.The ratio σM/σT is more preferably 1.7 or more, still more preferably1.8 or more.

The collector of the electrode for a non-aqueous electrolyte secondarybattery of the present invention may be formed of any electricallyconductive material. Accordingly, the collector can be formed of, forexample, a metal material such as aluminum, nickel, iron, stainlesssteel, titanium and copper, particularly aluminum, stainless steel orcopper.

[Non-Aqueous Electrolyte Secondary Battery]

The non-aqueous electrolyte secondary battery of the present inventionis a non-aqueous secondary battery containing the electrode for anon-aqueous electrolyte secondary battery of the present invention. Thenon-aqueous electrolyte secondary battery of the present invention hasexcellent cycle characteristics and high capacity by virtue ofcontaining the electrode for a non-aqueous electrolyte secondary batteryof the present invention.

The non-aqueous electrolyte secondary battery of the present inventionincludes, for example, a lithium ion secondary battery, a lithiumbattery, and a lithium ion polymer battery but is preferably a lithiumion secondary battery. In the non-aqueous electrolyte secondary batteryof the present invention, a positive electrode obtained by forming apositive electrode active material layer on a surface of a collector, anelectrolyte layer containing an electrolyte, and the negative electrodefor a non-aqueous electrolyte secondary battery of the present inventionmay be stacked such that the positive electrode active material layerand the negative electrode active material layer of the negativeelectrode of the present invention face each other and the electrolytelayer is inserted between the positive electrode active material layerand the negative electrode active material according to the presentinvention.

Alternatively, in the non-aqueous electrolyte secondary battery of thepresent invention, the positive electrode for a non-aqueous electrolytesecondary battery of the present invention, an electrolyte layercontaining an electrolyte, and a negative electrode obtained by forminga negative electrode active material layer on a surface of a collectormay be stacked such that the positive electrode active material layer ofthe positive electrode of the present invention and the negativeelectrode active material layer of the negative electrode face eachother and the electrolyte layer is inserted between the positiveelectrode active material layer of the positive electrode of the presentinvention and the negative electrode active material layer. Furthermore,in the non-aqueous electrolyte secondary battery of the presentinvention, the positive electrode for a non-aqueous electrolytesecondary battery of the present invention, an electrolyte layercontaining an electrolyte, and the negative electrode for a non-aqueouselectrolyte secondary battery of the present invention may be stackedsuch that the positive electrode active material layer of the positiveelectrode of the present invention and the negative electrode activematerial layer of the negative electrode of the present invention faceeach other and the electrolyte layer is inserted between the positiveelectrode active material of the positive electrode of the presentinvention and the negative electrode active material layer of thenegative electrode of the present invention.

The electrolyte layer for the non-aqueous electrolyte secondary batteryof the present invention is not limited as long as the object andeffects of the present invention are not impaired. Accordingly, as theelectrolyte layer, for example, a liquid electrolyte, i.e., a solutionprepared, for example, by dissolving a lithium salt in an organicsolvent, may be used. However, in the case of using such a liquidelectrolyte, a separator composed of a porous layer is preferably usedin general so as to prevent direct contact between the positiveelectrode active material layer and the negative electrode activematerial layer.

As the organic solvent for the liquid electrolyte, for example, ethylenecarbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC),dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) may be used.One of these organic solvents may be used alone, or two or more thereofmay be used in combination. As the lithium salt for the liquidelectrolyte, for example, LiPF₆, LiClO₄, LiN(CF₃SO₂)₂, and LiBF₄ can beused. One of these lithium salts may be used alone, or two or morethereof may be used in combination.

Incidentally, a solid electrolyte may also be used for the electrolytelayer and in this case, a separate spacer can be omitted.

<Fourth Aspect of the Present Invention>

The present invention is described below.

The ultrafine-fibrous-carbon aggregates of the present invention isultrafine-fibrous-carbon aggregates obtained by aggregating ultrafinefibrous carbons having a linear structure, wherein at least a part ofthe surface of the ultrafine fibrous carbons in at least a part of theultrafine-fibrous-carbon aggregates is modified with a surfactant and/orat least a part of the surface of the ultrafine fibrous carbons in atleast a part of the ultrafine-fibrous-carbon aggregates is oxidativelytreated, and, in the fiber length distribution of theultrafine-fibrous-carbon aggregates, which is obtained by measuring thevolume-based particle size distribution, a first peak exists at a fiberlength of 15 μm or less and a second peak exists at a fiber length ofmore than 15 μm, and the ratio of the volume-based particle sizedistribution (%) of the first peak to the volume-based particle sizedistribution (%) of the second peak is 3/1 or more (embodiment 1).

The ultrafine fibrous carbons of the present invention has excellentwater dispersibility and excellent mechanical strength due to aconfiguration where at least a part of the surface of the ultrafinefibrous carbons is modified with a surfactant, at least a part of thesurface of the ultrafine fibrous carbons is oxidatively treated, or atleast a part of the surface of the ultrafine fibrous carbons is modifiedwith a surfactant and oxidatively treated, and, in the volume-basedfiber length distribution of the ultrafine-fibrous-carbon aggregates,which is obtained by measuring the volume-based particle sizedistribution, a first peak exists at a fiber length of 15 μm or less,and a second peak exists at a fiber length of more than 15 μm, and theratio of the volume-based particle size distribution (%) of the firstpeak to the volume-based particle size distribution (%) of the secondpeak is 3/1 or more.

Here, “in the volume-based fiber length distribution of theultrafine-fibrous-carbon aggregates, which is obtained by measuring thevolume-based particle size distribution, a first peak exists at a fiberlength of 15 μm or less and a second peak exists at a fiber length ofmore than 15 μm, and the ratio of the volume-based particle sizedistribution (%) of the first peak to the volume-based particle sizedistribution (%) of the second peak is . . . ” can be determined asfollows. In a chart obtained by measuring the volume-based particle sizedistribution of the ultrafine-fibrous-carbon aggregates by means of aparticle size distribution meter (the abscissa is the fiber length andthe ordinate is the volume-based particle size distribution (%)), apoint having a largest volume-based particle size distribution (%) outof points causing the gradient to greatly change in the region of afiber length of 15 μm or less is designated as a first peak, a pointhaving a largest volume-based particle size distribution (%) out ofpoints causing the gradient to greatly change in the region of a fiberlength of more than 15 μm is designated as a second peak, and the ratio(first peak/second peak) between the volume-based particle sizedistribution (%) of the first peak and the volume-based particle sizedistribution (%) of the second peak is determined.

The “point causing the gradient to greatly change” indicates, other thanthe maximum value, a point not showing a distinct maximum value butcausing the gradient to greatly change around the point, for example, asecond peak shown in FIG. 41 or 42.

In embodiment 1, the ultrafine-fibrous-carbon aggregates of the presentinvention are ultrafine-fibrous-carbon aggregates where the averagefiber length of the ultrafine fibrous carbons in theultrafine-fibrous-carbon aggregates is 25 μm or less (embodiment 2).According to embodiment 2, the water dispersibility and mechanicalstrength of the ultrafine-fibrous-carbon aggregates of the presentinvention are more improved.

In embodiment 1 or 2, the ultrafine-fibrous-carbon aggregates of thepresent invention are ultrafine-fibrous-carbon aggregates, which areformed through a treatment in an ultra-centrifugal mill (embodiment 3).According to embodiment 3, the water dispersibility and mechanicalstrength of the ultrafine-fibrous-carbon aggregates of the presentinvention are more improved.

In any one embodiment of embodiments 1 to 3, theultrafine-fibrous-carbon aggregates of the present invention isultrafine-fibrous-carbon aggregates where the aspect ratio of theultrafine fibrous carbons in the ultrafine-fibrous-carbon aggregates isfrom 1 to 1,000 (embodiment 4).

The carbon-based electroconductive agent of the present invention is acarbon-based electroconductive agent containing theultrafine-fibrous-carbon aggregates in any one embodiment of embodiments1 to 4 (embodiment 5). According to embodiment 5, the carbon-basedelectroconductive agent of the present invention has excellentelectrically conductivity, i.e., high electrical conductivity, andexcellent mechanical strength.

The electrode material for a non-aqueous electrolyte secondary batteryof the present invention is an electrode material for a non-aqueouselectrolyte secondary battery, containing at least the carbon-basedelectroconductive agent of embodiment 5, an electrode active material,and a binder (embodiment 6). According to embodiment 6, the electrodematerial for a non-aqueous electrolyte secondary battery of the presentinvention has excellent electrically conductivity, i.e., high electricalconductivity, and excellent mechanical strength.

In embodiment 6, the electrode material for a non-aqueous electrolytesecondary battery of the present invention is an electrode material fora non-aqueous electrolyte secondary battery, which further containswater as a solvent (embodiment 7). According to embodiment 7, the waterdispersibility of the ultrafine-fibrous-carbon aggregates is moreimproved, and the electrode material for a non-aqueous electrolytesecondary battery of the present invention has higher electricalconductivity and more excellent mechanical strength.

The electrode for a non-aqueous electrolyte secondary battery of thepresent invention is an electrode for a non-aqueous electrolytesecondary battery, having a collector and an active material layer onthe collector, wherein the active material layer is composed of theelectrode material for a non-aqueous electrolyte secondary battery ofembodiment 6 or 7 (embodiment 8). According to embodiment 8, theelectrode for a non-aqueous electrolyte secondary battery of the presentinvention has excellent electrically conductivity, i.e., high electricalconductivity, and excellent mechanical strength.

The non-aqueous electrolyte secondary battery of the present inventionis a non-aqueous electrolyte secondary battery containing the electrodefor a non-aqueous electrolyte secondary battery of embodiment 8(embodiment 9). The water dispersibility and mechanical strength of theultrafine-fibrous-carbon aggregates are improved and in turn, thenon-aqueous electrolyte secondary battery of the present invention hasexcellent cycle characteristics and high capacity.

The ultrafine-fibrous-carbon aggregates of the present invention may beultrafine-fibrous-carbon aggregates where at least two embodiments outof embodiments 1 to 4 are arbitrarily combined. The carbon-basedelectroconductive agent of the present invention may contain thisultrafine-fibrous-carbon aggregates, the electrode material for anon-aqueous electrolyte secondary battery of the present invention maycontain this carbon electroconductive agent, the electrode for anon-aqueous electrolyte secondary battery of the present invention maycontain this electrode material for a non-aqueous electrolyte secondarybattery, and the non-aqueous electrolyte secondary battery of thepresent invention may contain this electrode for a non-aqueouselectrolyte secondary battery.

The present invention is described in more detail below.

[Ultrafine-Fibrous-Carbon Aggregates]

The ultrafine-fibrous-carbon aggregates of the present invention isultrafine-fibrous-carbon aggregates obtained by aggregating ultrafinefibrous carbons having a linear structure, wherein at least a part ofthe surface of the ultrafine fibrous carbons in at least a part of theultrafine-fibrous-carbon aggregates is modified with a surfactant and/orat least a part of the surface of the ultrafine fibrous carbons in atleast a part of the ultrafine-fibrous-carbon aggregates is oxidativelytreated and in the fiber length distribution of theultrafine-fibrous-carbon aggregates, which is obtained by measuring thevolume-based particle size distribution and which has a first peak at afiber length of 15 μm or less and a second peak at a fiber length ofmore than 15 μm, the ratio of the volume-based particle sizedistribution (%) of the first peak to the volume-based particle sizedistribution (%) of the second peak is 3/1 or more.

The linear structure as used herein means that the branching degree is0.01 branch/μm or less. The branching indicates a granular part formedby bonding of ultrafine fibrous carbons to another ultrafine fibrouscarbons at a position other than the terminal part and indicates thatthe primary axis of the ultrafine fibrous carbons is diverged inmidstream and the primary axis of the ultrafine fibrous carbons has abranching secondary axis.

The ultrafine-fibrous-carbon aggregates of the present invention hasexcellent water dispersibility due to a configuration where a part orthe entirety of the surface of the ultrafine fibrous carbons in at leasta part of the ultrafine-fibrous-carbon aggregates is modified with asurfactant. In addition, the ultrafine fibrous carbons of the presentinvention has excellent water dispersibility due to a configurationwhere a part or the entirety of the surface of the ultrafine fibrouscarbons is oxidatively treated. A part of the surface of the ultrafinefibrous carbons includes, for example, the surface at an edge of theultrafine fibrous carbon. The water dispersibility means the degree ofdispersion, i.e., dispersibility, of the ultrafine fibrous carbons in anaqueous solution or water (e.g., ion-exchanged water).

Modifying at least a part of the surface of the ultrafine fibrouscarbons with a surfactant means to cause chemical modification, physicalmodification, or chemical modification and further physicalmodification, between the ultrafine fibrous carbons and a surfactant.Chemical modification means that the ultrafine fibrous carbons and asurfactant undergo a chemical reaction and are thereby chemicallybonded, and means, for example, that a functional group of the ultrafinefibrous carbons and a functional group of the surfactant are covalentlybonded. Physical modification means not chemical bonding but physicalbonding and means, for example, that a surfactant is adsorbed or adheredto the ultrafine fibrous carbon.

The surfactant for modifying the ultrafine fibrous carbons includes, forexample, an anionic surfactant (e.g., sodium carboxymethyl cellulose(CMC-Na), sodium fatty acid, sodium alkylbenzenesulfonate), an cationicsurfactant (e.g., alkyltrimethylammonium salt, dialkyldimethylammoniumsalt), an amphoteric surfactant (e.g., alkyldimethylamine oxide,alkylcarboxybetaine), and a nonionic surfactant (e.g., polyoxyethylenealkyl ether, fatty acid diethanolamide), with sodium carboxymethylcellulose (CMC-Na) being preferred.

The mass ratio between the ultrafine fibrous carbons and the surfactantfor modifying the ultrafine fibrous carbons is not particularly limitedas long as the object of the present invention is achieved andfurthermore, the effects of the present invention are produced, but themass ratio is preferably 5:6.

Specific examples of the oxidative treatment applied to at least a partof the surface of the ultrafine fibrous carbons include an oxidativetreatment with peroxide (H₂O₂), an oxidative treatment with ozone, anoxidative treatment by UV irradiation, and an oxidative treatment inair. From the standpoint that an ionic carboxyl group is produced on thesurface of the ultrafine fibrous carbons of the present invention by anoxidative treatment with peroxide (H₂O₂), an oxidative treatment withperoxide (H₂O₂) is preferred.

The ultrafine-fibrous-carbon aggregates of the present invention hasexcellent water dispersibility and excellent mechanical strength due toa configuration where, in the volume-based fiber length distribution ofthe ultrafine-fibrous-carbon aggregates, which is obtained by measuringthe volume-based particle size distribution, a first peak exists at afiber length of 15 μm or less and a second peak exists at a fiber lengthof more than 15 μm, and the ratio of the volume-based particle sizedistribution (%) of the first peak to the volume-based particle sizedistribution (%) of the second peak is 3/1 or more. The ultrafinefibrous carbons having a fiber length of 15 μm or less constituting theultrafine-fibrous-carbon aggregates of the present invention mainlycontributes to improvement of water dispersibility, and the ultrafinefibrous carbons having a fiber length of more than 15 μm constitutingthe ultrafine-fibrous-carbon aggregates of the present invention mainlycontributes to improvement of mechanical strength (reinforcementeffect).

Furthermore, in the present invention, the mechanical strength in thecoating direction for coating the electrode material (MD direction)and/or the in-plane direction perpendicular to the coating direction (TDdirection) is large by virtue of containing ultrafine fibrous carbonshaving a fiber length of 15 μm or less and ultrafine fibrous carbonshaving a fiber length of more than 15 μm, so that an excellentreinforcement effect can be provided.

In the ultrafine-fibrous-carbon aggregates of the present invention, theratio of the volume-based particle size distribution (%) of the firstpeak at a fiber length of 15 μm or less to the volume-based particlesize distribution (%) of the second peak at a fiber length of more than15 μm is 3/1 or more, preferably 5/1 or more. Due to this preferredembodiment, the water dispersibility and mechanical strength can be moreimproved. If the ratio of the volume-based particle size distribution(%) of the first peak at a fiber length of 15 μm or less to thevolume-based particle size distribution (%) of the second peak at afiber length of more than 15 μm is less than 3/1, the waterdispersibility and/or mechanical strength may not be improved.

The ultrafine-fibrous-carbon aggregates of the present inventionpreferably has a configuration where in the volume-based fiber lengthdistribution of the ultrafine-fibrous-carbon aggregates, which isobtained by measuring the volume-based particle size distribution, theratio of the ultrafine fibrous carbons having a fiber length of morethan 15 μm to 50 μm is less than 50 vol % relative to the ultrafinefibrous carbon. The ratio may be more preferably less than 40 vol %,less than 30 vol %, less than 20 vol %, or less than 10 vol %. Withinsuch a preferable range, the water dispersibility and mechanicalstrength can be further improved.

In the ultrafine-fibrous-carbon aggregates of the present invention, theaverage fiber length of the ultrafine fibrous carbons of theultrafine-fibrous-carbon aggregates may be from 1 to 100 μm but ispreferably 25 μm or less, more preferably 23 μm or less, still morepreferably 20 μm or less, yet still more preferably 18 μm or less. Dueto such a preferred embodiment, the water dispersibility and mechanicalstrength can be further improved. If the average fiber length of theultrafine fibrous carbons exceeds 100 μm, the water dispersibility andmechanical strength of the ultrafine-fibrous-carbon aggregates of thepresent invention may be impaired. In the description of the presentinvention, the ultrafine fibrous carbons is sometimes referred to asCNF, and the ultrafine fibrous carbons having a short average fiberlength, for example, ultrafine fibrous carbons having an average fiberlength of 1 to 10 μm, is sometimes referred to as S-CNF.

The ultrafine-fibrous-carbon aggregates of the present invention arepreferably formed through a treatment in an ultra-centrifugal mill. Dueto a treatment in an ultra-centrifugal mill, the water dispersibilityand mechanical strength of the ultrafine-fibrous-carbon aggregates ofthe present invention can be further improved. In an ultra-centrifugalmill, the ultrafine fibrous carbons of the present invention isinstantly pulverized by a treatment in two steps, i.e., impact grindingand shearing. More specifically, the ultrafine fibrous carbons chargedis blown by a centrifugal force of a rotor rotating at a high speed,thereby enabling the impact grinding, and furthermore, sheared by aring-shaped screen on the outer periphery of the rotor. Through thistreatment in an ultra-centrifugal mill, the ultrafine-fibrous-carbonaggregates of the present invention are formed. When the treatment intwo steps of impact grinding and shearing is designated as onetreatment, the ultrafine-fibrous-carbon aggregates of the presentinvention may be formed through any number of treatments in anultra-centrifugal mill but is preferably formed through 1 to 10treatments, more preferably formed through 1 treatment, still morepreferably formed through 5 or more treatments.

The ultrafine-fibrous-carbon aggregates of the present invention ispreferably formed by applying a graphitization treatment. Thegraphitization treatment may be applied before the treatment in anultra-centrifugal mill or may be applied after the treatment in anultra-centrifugal mill but is preferably applied after the treatment inan ultra-centrifugal mill. The graphitization treatment can be performedby a known method (for example, the method described in JP2012-36520A).The inert gas used for the graphitization treatment includes nitrogen,argon, etc., and the graphitization treatment temperature is preferablyfrom 500 to 3,500° C., more preferably from 2,000 to 3,500° C., stillmore preferably from 2,600 to 3,000° C. The graphitization treatmenttime may be any time as long as the graphitization can be achieved, butthe graphitization treatment time is preferably from 0.1 to 24 hours,more preferably from 0.2 to 10 hours, still more preferably from 0.5 to8 hours. Incidentally, the oxygen concentration at the time ofgraphitization treatment is preferably 20 ppm by volume or less, morepreferably 10 ppm by volume or less.

The ultrafine fibrous carbons of the present invention is preferablyultrafine fibrous carbons having an aspect ratio of 1 to 1,000, morepreferably ultrafine fibrous carbons having an aspect ratio of 5 to 500,still more preferably ultrafine fibrous carbons having an aspect ratioof 10 to 100.

The ultrafine fibrous carbons constituting the ultrafine-fibrous-carbonaggregates of the present invention is not particularly limited as longas the object of the present invention is achieved and furthermore, theeffects of the present invention are produced, but the ultrafine fibrouscarbons is preferably easily-graphitizable carbon. Theeasily-graphitizable carbon is a raw carbon material in which a graphitestructure having a three-dimensional lamination regularity is readilyproduced by heat treatment at a high temperature of 2,500° C. or more,and is also called soft carbon, etc. The easily-graphitizable carbonincludes petroleum coke, coal pitch coke, polyvinyl chloride,3,5-dimethylphenolformaldehyde resin, etc.

Above all, a compound capable of forming an optically anisotropic phase(liquid crystal phase) in a molten state, which is called a mesophasepitch, or a mixture thereof is preferred, because high crystallinity andhigh electrical conductivity are expected. The mesophase pitch includes,for example, a petroleum-based mesophase pitch obtained from a petroleumresidue oil by a method based on hydrogenation and heat treatment or bya method based on hydrogenation, heat treatment and solvent extraction;a coal-based mesophase pitch obtained from a coal tar pitch by a methodbased on hydrogenation and heat treatment or by a method based onhydrogenation, heat treatment and solvent extraction; and a syntheticliquid crystal pitch obtained by polycondensation in the presence of asuper strong acid (e.g., HF, BF3) by using, as a raw material, anaromatic hydrocarbon such as naphthalene, alkylnaphthalene andanthracene. Among these, a synthetic liquid crystal pitch is preferredin view of not containing impurities.

(Average Fiber Diameter)

The average fiber diameter of the ultrafine fibrous carbons constitutingthe ultrafine-fibrous-carbon aggregates of the present invention ispreferably from more than 200 nm to 900 nm. This average fiber diameteris a value measured from a photographic view taken at a magnification of2,000 times by a field emission scanning electron microscope. Theaverage fiber diameter of the ultrafine fibrous carbons is preferablyfrom more than 230 nm to 600 nm, more preferably from more than 250 nmto 500 nm, still more preferably from more than 250 nm to 400 nm.

(Average Interplanar Spacing)

The average interplanar spacing of the ultrafine fibrous carbonsconstituting the ultrafine-fibrous-carbon aggregates of the presentinvention is not particularly limited as long as the object of thepresent invention is achieved and furthermore, the effects of thepresent invention are produced, but the average interplanar spacingd(002) of (002) plane as measured by an X-ray diffraction method ispreferably from 0.335 to 0.340 nm.

Here, FIG. 40 shows a scanning electron micrograph (2,000 timesmagnification) of a representative ultrafine fibrous carbonsconstituting the ultrafine-fibrous-carbon aggregates of the presentinvention. As evident from FIG. 40, it is confirmed that the ultrafinefibrous carbons has a linear structure and the average fiber length isfrom 1 to 100 μm.

The ultrafine fibrous carbons (CNF or S-CNF) constituting theultrafine-fibrous-carbon aggregates of the present invention areproduced by a known production method. For example, the ultrafinefibrous carbons (CNF or S-CNF) can be produced by the production methoddescribed in JP2010-13742A, JP2010-31439A, etc. Then, theultrafine-fibrous-carbon aggregates of the present invention are formedby aggregating the ultrafine fibrous carbons produced above.

[Electroconductive Agent]

The carbon-based electroconductive agent of the present invention is acarbon-based electroconductive agent containing theultrafine-fibrous-carbon aggregates of the present invention. Thecarbon-based electroconductive agent of the present invention hasexcellent electrical conductivity, i.e., high electrical conductivity,and excellent mechanical strength by virtue of containing theultrafine-fibrous-carbon aggregates of the present invention. Thecarbon-based electroconductive agent of the present invention containsthe ultrafine-fibrous-carbon aggregates of the present invention and aslong as the electrical conductivity can be enhanced, may further containa material other than the ultrafine-fibrous-carbon aggregates of thepresent invention, for example, a carbon-based material.

[Electrode Material for Non-Aqueous Electrolyte Secondary Battery]

The electrode material for a non-aqueous electrolyte secondary batteryof the present invention is an electrode material for a non-aqueouselectrolyte secondary battery, containing at least the carbon-basedelectroconductive agent of the present invention, an electrode activematerial, and a binder. The electrode material for a non-aqueouselectrolyte secondary battery of the present invention has excellentelectrical conductivity, i.e., high electrical conductivity, andexcellent mechanical strength by virtue of containing the carbon-basedelectroconductive agent of the present invention.

The electrode material for a non-aqueous electrolyte secondary batteryof the present invention preferably further contains water as a solvent.Water as the solvent includes, for example, ion-exchanged water. Byfurther containing water as a solvent, the water dispersibility of theultrafine-fibrous-carbon aggregates of the present invention is moreimproved, and the electrode material for a non-aqueous electrolytesecondary battery of the present invention has higher electricalconductivity.

The electrode active material (positive electrode active material andnegative electrode active material) contained in the electrode materialfor a non-aqueous electrolyte secondary battery of the present inventionis described below.

(Positive Electrode Active Material)

As the positive electrode active material contained in the electrodematerial for a non-aqueous electrolyte secondary battery of the presentinvention, any one member or two or more members appropriately selectedfrom the materials conventionally known as the positive electrode activematerial in a non-aqueous electrolyte secondary battery may be used. Forexample, in the case of a lithium ion secondary battery, alithium-containing metal oxide capable of storing/releasing lithium ionis suitable. The lithium-containing metal oxide includes a compositeoxide containing lithium and at least one element selected from thegroup consisting of Co, Mg, Mn, Ni, Fe, Al, Mo, V, W, Ti, etc.

Specifically, the composite oxide includes at least one member selectedfrom the group consisting of Li_(x)CoO₂, Li_(x)NiO₂, Li_(x)MnO₂,Li_(x)Co_(a)Ni_(1-a)O₂, Li_(x)Co_(b)V_(1-b)O_(z),Li_(x)Co_(b)Fe_(1-b)O₂, Li_(x)Mn₂O₄, Li_(x)Mn_(c)Co_(2-c)O₄,Li_(x)Mn_(c)Ni_(2-c)O₄, Li_(x)Mn_(c)V_(2-c)O₄, Li_(x)Mn_(c)Fe_(2-c)O₄(wherein x=from 0.02 to 1.2, a=from 0.1 to 0.9, b=from 0.8 to 0.98,c=from 1.6 to 1.96, and z=from 2.01 to 2.3), etc. Preferablelithium-containing metal oxides include at least one member selectedfrom the group consisting of Li_(x)CoO₂, Li_(x)NiO₂, Li_(x)MnO₂,Li_(x)Co_(a)Ni_(1-a)O₂, Li_(x)Mn₂O₄, and Li_(x)Co_(b)V_(1-b)O_(z) (wherex, a, b and z are the same as above). Incidentally, the value of x is avalue before start of charging/discharging and is increased/decreased bycharging/discharging.

As for the positive electrode active material above, one material may beused alone, or two or more materials may be used in combination. Theaverage particle diameter of the positive electrode active material is10 μm or less. If the average particle diameter exceeds 10 μm, theefficiency of charge/discharge reaction under a large current decreases.The average particle diameter is preferably from 0.05 μm (50 nm) to 7μm, more preferably from 1 to 7 μm.

(Negative Electrode Active Material)

As the negative electrode active material contained in the electrodematerial for a non-aqueous electrolyte secondary battery of the presentinvention, one member or two or more members selected from the materialsconventionally known as the negative electrode active material in anon-aqueous electrolyte secondary battery may be used. For example, inthe case of a lithium ion secondary battery, a carbon material capableof storing/releasing lithium ion, either Si or Sn, an alloy or oxidecontaining at least either one thereof, etc. may be used. Among these, acarbon material is preferred.

Representative examples of the carbon material include natural graphite,artificial graphite produced by heat-treating petroleum-based andcoal-based cokes, hard carbon in which a resin is carbonized, and amesophase pitch-based carbon material. In the case of using naturalgraphite or artificial graphite, from the standpoint of increasing thebattery capacity, those having a graphite structure in which theinterplanar spacing d(002) of (002) plane is from 0.335 to 0.337 nm asmeasured by powder X-ray diffraction are preferred.

The natural graphite means a graphitic material naturally produced as anore. The natural graphite is classified, by its appearance and nature,into two types, i.e., scaly graphite having a high degree ofcrystallization and amorphous graphite having a low degree ofcrystallization. The scaly graphite is further classified into flakygraphite taking on a leaf-like appearance and scaly graphite taking on ablock-like appearance. The natural graphite working out to a graphiticmaterial is not particularly limited in its locality, nature, and kind.In addition, natural graphite or a particle produced using naturalgraphite as a raw material may be heat-treated before use.

The artificial graphite means graphite produced by a wide range ofartificial techniques or a graphitic material close to a perfectgraphite crystal. Representative examples thereof include those producedthrough a calcination step at approximately from 500 to 1,000° C. and agraphitization step at 2,000° C. or more by using, as a raw material,tar or coke obtained from a residue, etc. after coal carbonization orcrude oil distillation. In addition, Kish graphite obtained byreprecipitating carbon from molten iron is also a kind of artificialgraphite.

Other than the carbon material, when an alloy containing at least eitherone of Si and Sn is used as the negative electrode active material, thisis effective in that the electric capacity can be reduced, compared witha case of using Si or Sn as an elemental substance or using an oxidethereof. Particularly an Si-based alloy is preferred.

The Si-based alloy includes, for example, an alloy of Si and at leastone element selected from the group consisting of B, Mg, Ca, Ti, Fe, Co,Mo, Cr, V, W, Ni, Mn, Zn, Cu, etc. Specifically, the alloy includes atleast one member selected from the group consisting of SiB₄, SiB₆,Mg₂Si, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu5Si, FeSi₂,MnSi₂, VSi₂, WSi₂, ZnSi₂, etc.

In the present invention, as the negative electrode active material, oneof the above-described materials may be used alone, or two or morethereof may be used in combination. The average particle diameter of thenegative electrode active material is 10 μm or less. If the averageparticle diameter exceeds 10 μm, the efficiency of charge/dischargereaction decreases under a large current. The average particle diameteris preferably from 0.1 to 10 μm, more preferably from 1 to 7 p.m.

(Binder)

As for the binder contained in the non-aqueous electrolyte secondarybattery of the present invention, a binder enabling electrode moldingand having sufficient electrochemical stability can be suitably used. Assuch a binder, one or more members selected from the group consisting ofpolyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose,polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),synthetic butadiene rubber (SBR), a fluoroolefin copolymer crosslinkedpolymer, polyimide, petroleum pitch, coal pitch, a phenol resin, etc.are preferably used, and polyvinylidene fluoride (PVDF) is morepreferred.

The form at the time of use as a binder is not particularly limited andmay be a solid form or a liquid form (e.g., emulsion form), and the formcan be appropriately selected by taking into account, for example, theproduction method (in particular, whether dry kneading or wet kneading)of electrode and the solubility in electrolytic solution.

The solvent for dissolving the binder is not particularly limited aslong as it dissolves the binder. Specifically, the solvent includes, forexample, one or more kinds of solvents selected from the groupconsisting of N-methylpyrrolidone (NMP), dimethylacetamide (DMAc),dimethylformamide (DMF), dimethylsulfoxide (DMSO), etc. Particularly NMPor DMAc is preferred.

[Electrode for Non-Aqueous Electrolyte Secondary Battery]

The electrode for a non-aqueous electrolyte secondary battery of thepresent invention is an electrode for a non-aqueous electrolytesecondary battery, having a collector and an active material layer onthe collector, wherein the active material layer is composed of theelectrode material for a non-aqueous electrolyte secondary battery ofthe present invention. The electrode for a non-aqueous electrolytesecondary battery of the present invention is a positive electrode whenhaving a positive electrode active material layer on the collector andis a negative electrode when having a negative electrode active materiallayer on the collector. The electrode for a non-aqueous electrolytesecondary battery of the present invention has excellent electricalconductivity, i.e., high electrical conductivity, and excellentmechanical strength by virtue of containing, as an active materiallayer, the electrode material for a non-aqueous electrolyte secondarybattery of the present invention. The ultrafine-fibrous-carbonaggregates of the present invention has excellent water dispersibility,and therefore the electrode material for a non-aqueous electrolytesecondary battery of the present invention is easily formed into a pastewhen slurried, so that the electrode for a non-aqueous electrolytesecondary battery of the present invention can be easily produced.

As the method for manufacturing the electrode of a non-aqueouselectrolyte secondary battery of the present invention, the followingtwo techniques are employed in general. One method is a method where anelectrode active material, an electroconductive agent and a binder aremixed/kneaded and shaped into a film by extrusion molding, and theobtained film is rolled, stretched and then laminated together with acollector. Another method is a method where an electrode activematerial, an electroconductive agent, a binder and a solvent fordissolving the binder are mixed to prepare a slurry and the slurry iscoated on a substrate and after removing the solvent, pressed.

In the present invention, either method may be used, but since thelatter method is preferred, the latter method is described in detailbelow.

In the manufacture of the electrode for a non-aqueous electrolytesecondary battery of the present invention, the ratio of theelectroconductive agent of the present invention added in the slurry is10 mass % or less relative to the electrode material for a non-aqueouselectrolyte secondary battery of the present invention, which iscomposed of the electrode active material, the electroconductive agentand the binder. The adding ratio is preferably 7 mass % or less, morepreferably 5 mass % or less. If the ratio of the electroconductive agentadded exceeds 10 mass %, when fabricating a cell having any capacity,the amount of the active material in the electrode is reduced, leadingto difficulty of application to power source usage where high importanceis attached to the energy density.

In the present invention, the ratio of the binder added is from 1 to 25mass % relative to the electrode material composed of the electrodeactive material, the electroconductive agent and the binder. The addingratio is preferably from 3 to 20 mass %, more preferably from 5 to 20mass %. If the amount of the binder is less than 1 mass %, generation ofcracking or separation of the electrode from the collector may occur. Ifthe amount of the binder exceeds 25 mass %, when fabricating a cellhaving any capacity, the amount of the active material in the electrodeis reduced, leading to difficulty of application to power source usagewhere high importance is attached to the energy density.

At the time of manufacture of the electrode, because of poor dispersionstate in the slurry, it is sometimes difficult to ensure fluiditysuitable for coating. In such a case, a slurrying aid may be used. Theslurrying aid includes, for example, one or more members selected fromthe group consisting of polyvinylpyrrolidone, carboxymethyl cellulose,polyvinyl acetate, polyvinyl alcohol, etc. Particularly use ofpolyvinylpyrrolidone is preferred. By adding the above-describedslurrying aid, sufficient fluidity can be ensured even with a relativelysmall amount of a solvent, and the dispersibility of pulverized activecarbon is also dramatically enhanced. In addition, generation ofcracking after the removal of solvent can be reduced.

The solid content concentration in the slurry (the ratio of the totalweight of the slurry components other than the solvent to the total massof the slurry) is preferably from 10 to 50 mass %, more preferably from15 to 40 mass %. If the solid content concentration exceeds 50 mass %,it may be difficult to manufacture a uniform slurry. If this value isless than 10 mass %, the slurry viscosity may be decreased too much,resulting in uneven thickness of the electrode.

For coating the slurry, for example, an appropriate coating method suchas doctor blade may be employed. After the coating, the solvent isremoved by a treatment, for example, at 60 to 150° C., preferably from75 to 85° C., for preferably from 60 to 180 minutes. Thereafter, thecoated material after the removal of solvent is pressed, whereby anactive material layer can be produced.

In the electrode for a non-aqueous electrolyte secondary battery of thepresent invention, the thickness of the active material layer issuitably from 5 to 300 μm. If the thickness of the active material layeris less than 5 μm, when fabricating a cell having any capacity, aseparator or a collector needs to be used in a large amount, leading toa decrease in the volume occupancy of the active material layer in thecell, and not only this is disadvantageous in view of energy density butalso the usage is considerably limited. In particular, although outputcharacteristics (including low-temperature characteristics) areimportant, application to power source usage where high importance isattached to energy density becomes difficult.

On the other hand, production of an electrode where the electrodethickness exceeds 300 μm is relatively difficult due to problem of crackgeneration. Therefore, the electrode thickness is in general preferably300 μm or less in view of stable production of the electrode. In orderto more stably produce the electrode, the electrode thickness is morepreferably 200 μm or less and for the purpose of elevating theproductivity of electrode or the output characteristics of capacitor,the electrode thickness is still more preferably from 10 to 100 μm.

The electrode for a non-aqueous electrolyte secondary battery accordingto the present invention, which is manufactured as above, preferably hasno anisotropy of mechanical strength (electrode strength) in view ofreinforcement effect. In the electrode having no anisotropy ofmechanical strength (electrode strength), from which the collector isremoved, i.e., in the electrode material for a non-aqueous electrolytesecondary battery of the present invention, the ratio σM/σT between thetensile strength σM in the coating direction for coating the electrodematerial and the in-plane tensile strength σ_(T) in the directionperpendicular to the direction of the coating direction is preferably1.6 or less. The ratio σM/σT is more preferably 1.2 or less, still morepreferably from 0.9 to 1.1.

The electrode for a non-aqueous electrolyte secondary battery of thepresent invention, which is manufactured as above, preferably hasanisotropy of mechanical strength (electrode strength) in view ofreinforcement effect. In the electrode having anisotropy of mechanicalstrength (electrode strength), from which the collector is removed,i.e., in the electrode material for a non-aqueous electrolyte secondarybattery of the present invention, the ratio σM/σT between the tensilestrength σM in the coating direction for coating the electrode materialand the in-plane tensile strength σ_(T) in the direction perpendicularto the direction of the coating direction is preferably more than 1.6.The ratio σM/σT is more preferably 1.7 or more, still more preferably1.8 or more.

The collector of the electrode for a non-aqueous electrolyte secondarybattery of the present invention may be formed of any electricallyconductive material. Accordingly, the collector can be formed of, forexample, a metal material such as aluminum, nickel, iron, stainlesssteel, titanium and copper, particularly aluminum, stainless steel orcopper.

[Non-Aqueous Electrolyte Secondary Battery]

The non-aqueous electrolyte secondary battery of the present inventionis a non-aqueous secondary battery containing the electrode for anon-aqueous electrolyte secondary battery of the present invention. Thenon-aqueous electrolyte secondary battery of the present invention hasexcellent cycle characteristics and high capacity by virtue ofcontaining the electrode for a non-aqueous electrolyte secondary batteryof the present invention.

The non-aqueous electrolyte secondary battery of the present inventionincludes, for example, a lithium ion secondary battery, a lithiumbattery, and a lithium ion polymer battery but is preferably a lithiumion secondary battery. In the non-aqueous electrolyte secondary batteryof the present invention, a positive electrode obtained by forming apositive electrode active material layer on a surface of a collector, anelectrolyte layer containing an electrolyte, and the negative electrodefor a non-aqueous electrolyte secondary battery of the present inventionmay be stacked such that the positive electrode active material layerand the negative electrode active material layer of the negativeelectrode of the present invention face each other and the electrolytelayer is inserted between the positive electrode active material layerand the negative electrode active material according to the presentinvention.

Alternatively, in the non-aqueous electrolyte secondary battery of thepresent invention, the positive electrode for a non-aqueous electrolytesecondary battery of the present invention, an electrolyte layercontaining an electrolyte, and a negative electrode obtained by forminga negative electrode active material layer on a surface of a collectormay be stacked such that the positive electrode active material layer ofthe positive electrode of the present invention and the negativeelectrode active material layer of the negative electrode face eachother and the electrolyte layer is inserted between the positiveelectrode active material layer of the positive electrode of the presentinvention and the negative electrode active material layer. Furthermore,in the non-aqueous electrolyte secondary battery of the presentinvention, the positive electrode for a non-aqueous electrolytesecondary battery of the present invention, an electrolyte layercontaining an electrolyte, and the negative electrode for a non-aqueouselectrolyte secondary battery of the present invention may be stackedsuch that the positive electrode active material layer of the positiveelectrode of the present invention and the negative electrode activematerial layer of the negative electrode of the present invention faceeach other and the electrolyte layer is inserted between the positiveelectrode active material of the positive electrode of the presentinvention and the negative electrode active material layer of thenegative electrode of the present invention.

The electrolyte layer for the non-aqueous electrolyte secondary batteryof the present invention is not limited as long as the object andeffects of the present invention are not impaired. Accordingly, as theelectrolyte layer, for example, a liquid electrolyte, i.e., a solutionprepared, for example, by dissolving a lithium salt in an organicsolvent, may be used. However, in the case of using such a liquidelectrolyte, a separator composed of a porous layer is preferably usedin general so as to prevent direct contact between the positiveelectrode active material layer and the negative electrode activematerial layer.

As the organic solvent for the liquid electrolyte, for example, ethylenecarbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC),dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) may be used.One of these organic solvents may be used alone, or two or more thereofmay be used in combination. As the lithium salt for the liquidelectrolyte, for example, LiPF₆, LiClO₄, LiN(CF₃SO₂)₂, and LiBF₄ can beused. One of these lithium salts may be used alone, or two or morethereof may be used in combination.

Incidentally, a solid electrolyte may also be used for the electrolytelayer and in this case, a separate spacer can be omitted.

EXAMPLES

The present invention is described more specifically below by referringto Examples, but the present invention is not limited thereto.

<First Aspect of the Present Invention>

Various measurements and analyses in Examples were performed accordingto the following methods.

(1) Measurements of Fiber Diameter and Fiber Length of Precursor MoldedBody and Ultrafine Fibrous Carbons and Confirmation of Shape of OtherCarbon-Based Electroconductive Agents

Observation and photographing were performed using a scanning electronmicroscope (S-2400, manufactured by Hitachi, Ltd.). As for the averagefiber diameter of the ultrafine fibrous carbon, etc., the fiber diameterwas measured at 20 portions randomly selected on the obtained electronmicrograph, and the average value of all measurement results (n=20) wasdefined as the average fiber diameter. The average fiber length wascalculated in the same manner.

(2) X-Ray Diffraction Measurement of Ultrafine Fibrous Carbon

In the X-ray diffraction measurement, the lattice spacing (d002) and thecrystallite size (Lc002) were measured in conformity with JIS R7651Method by using RINT-2100, manufactured by Rigaku Corporation.

(3) Tensile Test of Electrode Material

The electrode was cut into a width of 1 cm and evaluated for themechanical strength by performing a tensile test by a universal tensiletester (INSTRON 5500R, manufactured by Instron Japan Co., Ltd.). Testconditions were a grip length of 5 cm and a tensile speed of 1 mm/min,and evaluation was performed by comparing the stress applied at 0.2%(0.1 mm) elongation. In performing the tensile test of each electrode,the test was performed in each of the coating direction (MD) whencoating the slurry at the time of manufacture of the electrode and thein-plane direction perpendicular to the coating direction (TD direction)(n=5), and the tensile strength σ_(M) in the MD direction and thetensile strength σ_(T) in the TD direction were determined by taking anaverage value of all results.

<Production of Ultrafine Fibrous Carbon>

90 Parts by mass of high-density polyethylene (HI-ZEX (registeredtrademark) 5000SR, produced by Prime Polymer Co., Ltd.; melt viscosityat 350° C. and 600 s⁻¹: 14 Pa·s) as a thermoplastic resin and 10 partsby mass of synthetic mesophase pitch AR•MPH (produced by Mitsubishi GasChemical Company, Inc.) as a thermoplastic carbon precursor were meltkneaded by a same-direction twin-screw extruder (“TEM-26SS”,manufactured by Toshiba Machine Co., Ltd., barrel temperature: 310° C.,under nitrogen stream) to prepare a resin composition.

The resin composition above was spun from a spinneret at 390° C. by acylinder-type single-hole spinning machine to make a precursor moldedbody (a sea-island type composite fiber containing the thermoplasticcarbon precursor as an island component). The fiber diameter of theprecursor molded body was 300 μm. Subsequently, the precursor moldedbody was held at 215° C. for 3 hours in air by a hot-air drier to obtaina stabilized precursor molded body.

In a vacuum gas displacement furnace, the stabilized precursor moldedbody was then subjected to nitrogen purging, depressurization to 1 kPaand temperature elevation to 500° C. at a temperature rise rate of 5°C./min in the depressurized state and held at 500° C. for 1 hour toremove the thermoplastic resin and form a fibrous carbon precursor. Thefibrous carbon precursor was added to ion-exchanged water and pulverizedby means of a mixer for 2 minutes to manufacture a preliminarydispersion liquid having dispersed therein ultrafine fibrous carbonsprecursor at a concentration of 0.1 wt %. The preliminary dispersionliquid was treated using a wet jet mill (Star Burst Labo HJP-17007,manufactured by Sugino Machine Limited, chamber used: single nozzlechamber) under the conditions of a nozzle diameter of 0.17 mm and atreatment pressure of 100 MPa and by repeating the treatment 10 times, adispersion liquid of a fibrous carbon precursor was manufactured. Theobtained solvent liquid was filtered to manufacture a nonwoven fabrichaving dispersed therein a fibrous carbon precursor.

The nonwoven fabric having dispersed therein a fibrous carbon precursorwas subjected to temperature elevation from room temperature to 3,000°C. over 3 hours in an argon gas atmosphere to manufacture ultrafinefibrous carbons. The average fiber diameter of the obtained ultrafinefibrous carbons was 300 nm, the average fiber length was 16 μm, and abranching structure was not observed, in other words, a linear structurewas confirmed. In addition, the average interplanar spacing d002 of(002) plane as measured by an X-ray diffraction method was 0.3375 nm.FIG. 10 shows a scanning electron micrograph (2,000 times magnification)of the ultrafine fibrous carbons (CNF) produced.

Reference Example A1 Manufacture of Electrode Active Material Layer>

A slurry was manufactured by using 4 parts by mass of the ultrafinefibrous carbons (carbon-based electroconductive agent) (CNF) produced asabove, 81 parts by mass of a negative electrode active material(artificial graphite; MCMB, produced by Osaka Gas Chemicals Co., Ltd.),15 parts by mass of polyvinylidene fluoride (produced by KurehaCorporation) as a binder, and N-methylpyrrolidone as a solution. Themanufactured slurry was coated on a glass plate and dried andthereafter, the electrode active material layer was separated from theglass substrate and roll-pressed (50 kg/cm², 5 cm/min) to manufacture anelectrode active material layer.

Tensile Test of Evaluated Electrode Material and Results>

The tensile strength of the electrode active material layer manufacturedas above was evaluated and found to be 2.6 MPa in the MD direction and1.5 MPa in the TD direction, and thus, σ_(M)/σ_(T)=1.7, revealing areinforcement effect having anisotropy. FIG. 2 shows a stress-straincurve obtained as a result of the tensile test.

In the ultrafine fibrous carbons used in Reference Example A1, the ratioof the fiber length to the fiber diameter is large. Therefore, theultrafine fibrous carbons tend to be aligned in the MD direction at thetime of coating of the slurry, and a large reinforcement effect wasexhibited in the MD direction.

Example A2 Manufacture of Electrode Active Material Layer>

An electrode active material layer was manufactured by performing theoperation in the same manner as in Reference Example A1, except that theultrafine fibrous carbons used in Reference Example A1 was pulverized(Star Burst, manufactured by Sugino Machine Limited) and used asultrafine fibrous carbons having an average fiber length of 5 μm. FIG.11 shows a scanning electron micrograph ((a) 2,000 times or (b) 8,000times magnification) of the ultrafine fibrous carbons having an averagefiber length of 5 μm (S-CNF).

Tensile Test of Evaluated Electrode Active Material Layer and Results>

The mechanical strength was evaluated by a tensile test and found to be1.9 MPa in the MD direction and 1.7 MPa in the TD direction, and thus,σ_(M)/σ_(T)=1.1, revealing a reinforcement effect having no anisotropy.FIG. 3 shows a stress-strain curve obtained as a result of the tensiletest.

In the ultrafine fibrous carbons used in Example A2, the fiber length isshorter than that of the ultrafine fibrous carbons of Reference ExampleA1 and in turn, the ratio of the fiber length to the fiber diameter isrelatively small. Therefore, the ultrafine fibrous carbons are lesslikely to be aligned in the slurry coating direction and there is littleanisotropy in the tensile strength. As a result, a reinforcement effectwas exhibited not only in the MD direction but also in the TD direction.

Example A3 Manufacture of Electrode Active Material Layer>

An electrode active material layer was manufactured by performing theoperation in the same manner as in Reference Example A1, except that 2parts by mass of the ultrafine fibrous carbons used in Reference ExampleA1 and 2 parts by mass of the ultrafine fibrous carbons used in ExampleA2 were used as the carbon-based electroconductive agent. FIG. 13 showsa scanning electron micrograph ((a) 5,000 times or (b) 8,000 timesmagnification) of the electrode active material layer manufactured. Asevident from FIG. 13, it was confirmed that both the ultrafine fibrouscarbons (CNF) used in Reference Example A1 and the ultrafine fibrouscarbons (S-CNF) used in Example A2 are present.

Tensile Test of Evaluated Electrode Active Material Layer and Results>

The mechanical strength was evaluated by a tensile test and found to be2.6 MPa in the MD direction and 1.8 MPa in the TD direction, and thus,σ_(M)/σ_(T)=1.5, revealing a reinforcement effect having littleanisotropy. FIG. 4 shows a stress-strain curve obtained as a result ofthe tensile test.

A reinforcement effect was exhibited in both the MD and TD directions bycombining the ultrafine fibrous carbons used in Reference Example A1,which tends to be aligned in the MD direction at the time of coating ofthe slurry, with the ultrafine fibrous carbons used in Example A2, whichis less likely to be aligned in the MD direction.

Example A4 Manufacture of Electrode Active Material Layer>

An electrode active material layer was manufactured by performing theoperation in the same manner as in Reference Example A1, except that 2parts by mass of the ultrafine fibrous carbons used in Reference ExampleA1 and 2 parts by mass of acetylene black (AB) (DENKA BLACK, produced byDenki Kagaku Kogyo Kabushiki Kaisha) were used as the carbon-basedelectroconductive agent. FIG. 12 shows a scanning electron micrograph(8,000 times magnification) of acetylene black (AB) used. In addition,FIG. 14 shows a scanning electron micrograph ((a) 5,000 times or (b)8,000 times magnification) of the electrode active material layermanufactured. As evident from FIG. 14, it was confirmed that both theultrafine fibrous carbons (CNF) used in Reference Example A1 andacetylene black (AB) are present.

Tensile Test of Evaluated Electrode Active Material Layer and Results

The mechanical strength was evaluated by a tensile test and found to be2.0 MPa in the MD direction and 1.4 MPa in the TD direction, and thus,σ_(M)/σ_(T)=1.4, revealing a reinforcement effect having littleanisotropy. FIG. 5 shows a stress-strain curve obtained as a result ofthe tensile test.

Since the ultrafine fibrous carbons used in Reference Example A1 isused, the ultrafine fibrous carbons tends to be aligned in the MDdirection at the time of coating of the slurry, and a largereinforcement effect was exhibited in the MD direction.

Comparative Example A1 Manufacture of Electrode Active Material Layer>

An electrode active material layer was manufactured by performing theoperation in the same manner as in Reference Example A1, except that avapor grown carbon fiber (carbon fiber having a branching structure)(VGCF) was used in place of the ultrafine fibrous carbons used inReference Example A1.

Tensile Test of Evaluated Electrode Active Material Layer and Results>

The mechanical strength was evaluated by a tensile test and found to be0.96 MPa in the MD direction and 0.90 MPa in the TD direction, revealinga poor reinforcement effect irrespective of the MD direction or the TDdirection. FIG. 6 shows a stress-strain curve obtained as a result ofthe tensile test.

Comparative Example A2 Manufacture of Electrode Active Material Layer>

An electrode active material layer was manufactured by performing theoperation in the same manner as in Reference Example A1, except thatacetylene black (AB) (DENKA BLACK, produced by Denki Kagaku KogyoKabushiki Kaisha) was used in place of the ultrafine fibrous carbonsused in Reference Example A1.

Tensile Test of Evaluated Electrode Active Material Layer and Results>

The mechanical strength was evaluated by a tensile test and found to be1.1 MPa in the MD direction and 1.1 MPa in the TD direction, revealing apoor reinforcement effect irrespective of the direction. FIG. 7 shows astress-strain curve obtained as a result of the tensile test.

FIGS. 7 and 8 show the results (MD direction and TD direction) of thestress (MPa) applied at 0.2% (0.1 mm) elongation of the electrodematerial layers manufactured in Reference Example A1, Examples A2 to A4and Comparative Examples A1 and A2. In addition, specific values (MDdirection and TD direction) of the stress (MPa) applied at 0.2% (0.1 mm)elongation of the electrode material layers manufactured in ReferenceExample A1, Examples A2 to A4 and Comparative Examples A1 and A2 areshown in Table 1 below.

TABLE 1 Table A1: Electroconductive agent Stress at 0.2% (0.1 mm) (mass%) Elongation (MPa) CNF S-CNF AB VGCF TD MD MD/TD Reference 4 1.5 2.61.7 Example A1 Example A2 4 1.7 1.9 1.1 Example A3 2 2 1.8 2.6 1.4Example A4 2 2 1.4 2.0 1.4 Comparative 4 0.9 0.96 1.1 Example A1Comparative 4 1.1 1.1 1.0 Example A2

Since the electrode for a non-electrolyte secondary battery according tothe present invention is composed of the electrode active material layeraccording to the present invention and a collector, the mechanicalstrength of the electrode for a non-electrolyte secondary batteryaccording to the present invention is understood to produce the sameeffect as the mechanical strength based on the results obtained with theelectrode material for a non-electrolyte secondary battery according tothe present invention.

The results in the MD direction (the coating direction for coating theelectrode material (slurry) at the time of manufacture of the electrode)of the stress (MPa) applied at 0.2% (0.1 mm) elongation of the electrodematerial layers manufactured in Reference Example A1, Examples A2 to A4and Comparative Examples A1 and A2 are shown together in FIG. 8. Inaddition, the results in the TD direction (the in-plane directionperpendicular to the coating direction for coating the electrodematerial (slurry) at the time of manufacture of the electrode) of thestress (MPa) applied at 0.2% (0.1 mm) elongation of the electrodematerial layers manufactured in Reference Example A1, Examples A2 to A4and Comparative Examples A1 and A2 are shown together in FIG. 9.

Example A5 Manufacture of Negative Electrode>

A slurry was manufactured by using 2 parts by mass of the ultrafinefibrous carbons (S-CNF) having an average fiber length of 5 μm producedin Example A2, 91 parts by mass of a negative electrode active material(scaly graphite; trade name: MAGD, produced by Hitachi Chemical Company,Ltd.), 7 parts by mass of polyvinylidene fluoride (produced by KurehaCorporation) as a binder, and N-methylpyrrolidone as a solution. Themanufactured slurry was coated, dried and roll-pressed to manufacture anegative electrode. The electrode thickness was 75 μm, and the electrodedensity was 1.5 g/cm³.

The tensile strength of the negative electrode manufactured as above wasevaluated and found to be 1.5 MPa in the MD direction and 1.4 MPa in theTD direction, and thus, σ_(M)/σ_(T)=1.1, revealing a reinforcementeffect having little anisotropy.

Manufacture of Positive Electrode>

A slurry was manufactured by using 89 parts by mass of lithium cobaltate(LiCoO₂, produced by Nippon Chemical Industrial Co., Ltd.), 6 parts bymass of polyvinylidene fluoride as a binder, acetylene black (tradename: DENKA

BLACK, produced by Denki Kagaku Kogyo Kabushiki Kaisha) as anelectrically conductive material, and N-methylpyrrolidone as a solution.The manufactured slurry was coated, dried and roll-pressed tomanufacture a positive electrode. The electrode thickness was 82 μm, andthe electrode density was 3.0 g/cm³.

Fabrication of Cell>

A single-layer laminate cell was fabricated by using the positive andnegative electrodes prepared as above and a porous polyethylene film forthe separator and injecting an electrolytic solution composed of anethylene carbonate/ethyl methyl carbonate mixed solution (3/7 by mass,produced by Kishida Chemical Co., Ltd.) containing LiPF₆ at aconcentration of 1 mol/L, into a cell.

Evaluation of Cycle Characteristics>

The battery performance of the lithium ion secondary batterymanufactured by the procedure above was evaluated as follows.

[Charge/Discharge Conditions]

Using the cell fabricated as above, a charge/discharge test wasperformed by a charging/discharging device. The charge conditions were0.2 C constant-current charge until 4.2 V, then constant-voltage charge(0.02 C cut-off) and after a pause for 10 minutes, switchover todischarge. The discharge conditions were 0.2 C constant-currentdischarge until 2.75 V.

As a result of evaluation, the capacity maintenance ratio at 50th cyclewas 92.0%, revealing good cycle characteristics.

Example A6

An electrode and a lithium ion secondary battery were produced in thesame manner as in Example A5, except that a mixture of the ultrafinefibrous carbons (CNF) manufactured above and S-CNF (mass ratio: 1:1) wasused in place of S-CNF of Example A5.

The tensile strength of the negative electrode manufactured as above wasevaluated and found to be 1.8 MPa in the MD direction and 1.4 MPa in theTD direction, and thus, σ_(M)/σ_(T)=1.3, revealing a reinforcementeffect having little anisotropy.

The cycle characteristics of the battery manufactured as above wasevaluated, as a result, the capacity maintenance ratio at 50th cycle was92.5%, revealing good cycle characteristics.

Example A7

An electrode and a lithium ion secondary battery were produced in thesame manner as in Example A5, except that a mixture of the ultrafinefibrous carbons (CNF) manufactured above and acetylene black (AB) (DENKABLACK, produced by Denki Kagaku Kogyo Kabushiki Kaisha) (mass ratio:1:1) was used in place of S-CNF of Example A5.

The tensile strength of the negative electrode manufactured as above wasevaluated and found to be 1.5 MPa in the MD direction and 1.2 MPa in theTD direction, and thus, σ_(M)/σ_(T)=1.3, revealing a reinforcementeffect having little anisotropy.

The cycle characteristics of the battery manufactured as above wasevaluated, as a result, the capacity maintenance ratio at 50th cycle was91.5%, revealing good cycle characteristics.

Comparative Example A3

An electrode and a lithium ion secondary battery were produced in thesame manner as in Example A5, except that a vapor grown carbon fiber(carbon fiber having a branching structure) was used in place of S-CNFof Example A5.

The cycle characteristics of the battery manufactured as above wasevaluated, as a result, the capacity maintenance ratio at 50th cycle was90.7%, revealing poor cycle characteristics.

Comparative Example A4

An electrode and a lithium ion secondary battery were produced in thesame manner as in Example A5, except that acetylene black (AB) (DENKABLACK, produced by Denki Kagaku Kogyo Kabushiki Kaisha) was used inplace of S-CNF of Example A5.

The cycle characteristics of the battery manufactured as above wasevaluated, as a result, the capacity maintenance ratio at 50th cycle was89.5%, revealing poor cycle characteristics.

The results of Examples A5 to A7 and Comparative Examples A3 and A4 areshown together in Table A1 below.

TABLE 2 Table A2: Stress at 0.2% Electroconductive (0.1 mm) Capacityagent (mass %) Elongation (MPa) Main- S- MD/ tenance CNF CNF AB VGCF TDMD TD Ratio (%) Example 2 1.4 1.5 1.1 92.0 A5 Example 1 1 1.4 1.8 1.392.5 A6 Example 1 1 1.2 1.5 1.3 91.5 A7 Com- 4 0.90 0.96 1.1 90.7parative Example A3 Com- 4 1.1 1.1 1.0 89.5 parative Example A4

Second Aspect of the Present Invention>

The second aspect of the present invention is described morespecifically below by referring to Examples, but the present inventionis not limited thereto.

Various measurements in Examples were performed according to thefollowing methods.

The measurements of fiber diameter and fiber length of the ultrafinefibrous carbons and the X-ray diffraction measurement of ultrafinefibrous carbons were performed in the same manner as above.

Example B1 Example B1-1 Production of Ultrafine Fibrous Carbon>

90 Parts by mass of high-density polyethylene (HI-ZEX (registeredtrademark) 5000SR, produced by Prime Polymer Co., Ltd.; melt viscosityat 350° C. and 600 s⁻¹: 14 Pa·s) as a thermoplastic resin and 10 partsby mass of synthetic mesophase pitch AR•MPH (produced by Mitsubishi GasChemical Company, Inc.) as a thermoplastic carbon precursor were meltkneaded by a same-direction twin-screw extruder (“TEM-26SS”,manufactured by Toshiba Machine Co., Ltd., barrel temperature: 310° C.,under nitrogen stream) to prepare a resin composition.

The resin composition above was spun from a spinneret at 390° C. by acylinder-type single-hole spinning machine to make a precursor moldedbody (a sea-island type composite fiber containing the thermoplasticcarbon precursor as an island component). The fiber diameter of theprecursor molded body was 300 μm. Subsequently, the precursor moldedbody was held at 215° C. for 3 hours in air by a hot-air drier to obtaina stabilized precursor molded body.

In a vacuum gas displacement furnace, the stabilized precursor moldedbody was then subjected to nitrogen purging, depressurization to 1 kPaand temperature elevation to 500° C. at a temperature rise rate of 5°C./min in the depressurized state and held at 500° C. for 1 hour toremove the thermoplastic resin and form a fibrous carbon precursor. Thefibrous carbon precursor was added to ion-exchanged water and pulverizedby means of a mixer for 2 minutes to disperse the fibrous carbonprecursor at a concentration of 0.1 mass %.

The dispersed fibrous carbon precursor was subjected to temperatureelevation from room temperature to 3,000° C. over 3 hours in an argongas atmosphere to manufacture ultrafine fibrous carbons. The averagefiber diameter of the obtained ultrafine fibrous carbons was 300 nm, theaverage fiber length was 16 μm, and a branching structure was notobserved, in other words, a linear structure was confirmed. In addition,the average interplanar spacing d002 of (002) plane as measured by anX-ray diffraction method was 0.3375 nm. FIG. 16 shows a scanningelectron micrograph (2,000 times magnification) of the ultrafine fibrouscarbons (CNF) produced.

Wet Compounding>

1 Part by mass of the ultrafine fibrous carbons obtained above and 1part by mass of acetylene black (DENKA BLACK 75% pressed product,produced by Denki

Kagaku Kogyo Kabushiki Kaisha) were pulverized using an ethanol solutionby means of a wet pulverizer (THINKY MIXER ARV-310, manufactured byThinky Corporation) to obtain Composite 1-1 (20 g).

Example B1-2 Production of Ultrafine Fibrous Carbon>

Ultrafine fibrous carbons was obtained by exactly the same productionmethod as the production method of ultrafine fibrous carbons describedin Example B1-1.

Dry Compounding>

1 Part by mass of the ultrafine fibrous carbons produced as above and 1part by mass of acetylene black (DENKA BLACK 75% pressed product,produced by Denki Kagaku Kogyo Kabushiki Kaisha) were pulverized bymeans of a dry jet mill (A-O Jet Mill, manufactured by SeishinEnterprise Co., Ltd.) to obtain Composite 1-2 (20 g).

Example B1-3 Production of Ultrafine Fibrous Carbon>

Ultrafine fibrous carbons was obtained by exactly the same productionmethod as the production method of ultrafine fibrous carbons describedin Example B1-1.

Compounding by Mechanical Milling>

1 Part by mass of the ultrafine fibrous carbons produced as above and 1part by mass of acetylene black (DENKA BLACK 75% pressed product,produced by Denki Kagaku Kogyo Kabushiki Kaisha) were pulverized bymeans of a planetary ball mill apparatus (apparatus: P-7, manufacturedby Fritsch Japan Co., Ltd., ball used: zirconia-made ball of 10 mm indiameter) to obtain Composite 1-3 (20 g).

Comparative Example B1-1

Ultrafine fibrous carbons was obtained (20 g) by exactly the sameproduction method as the production method of ultrafine fibrous carbonsdescribed in Example B1-1.

Comparative Example B1-2

20 g of acetylene black (DENKA BLACK 75% pressed product, produced byDenki Kagaku Kogyo Kabushiki Kaisha) was prepared.

Example B2 Example B2-1

Observation and photographing of Composite 1-1 obtained in Example B1-1were performed using a scanning electron microscope (S-2400,manufactured by Hitachi, Ltd.). FIG. 17 (photographing magnification×500 times) and FIG. 18 (photographing magnification ×1,000 times) showthe photographic results of photographing. As evident from FIGS. 17 and18, although aggregated acetylene black is observed in parts, the shapeof the ultrafine fibrous carbons is not changed, and the ultrafinefibrous carbons and acetylene black are dispersed together and presentin such a manner that they are integrally attached to each other.

Example B2-2

Observation and photographing of Composite 1-2 obtained in Example B1-2were performed using a scanning electron microscope (S-2400,manufactured by Hitachi, Ltd.), similarly to Example B2-1. FIG. 19(photographing magnification ×500 times) and FIG. 20 (photographingmagnification ×1,000 times) show the photographic results ofphotographing. As evident from FIGS. 19 and 20, the shape of theultrafine fibrous carbons is not changed, and the ultrafine fibrouscarbons and acetylene black are uniformly mixed in such a manner thatacetylene black is hybridized around the ultrafine fibrous carbon. Itwas confirmed that the ultrafine fibrous carbons and acetylene black areintegrally attached to each other and uniformly mixed with each other.

Example B3 Example B3-1

The relationship between density and volume resistivity was examinedusing Composite 1-1 obtained in Example B1-1. In order to examine therelationship between density and volume resistivity, the density and thevolume resistivity were measured using a four probe method (Loresta-GP,manufactured by Mitsubishi Chemical Analytech Co., Ltd.). A powdersample of Composite 1-1 was charged into Loresta-GP, and the volumeresistivity was measured while decreasing the density value by crushingthe powder from above at ordinary temperature to apply a pressure. FIG.21 shows the measurement results. For example, when the density is 0.58g/cc, the volume resistivity of Composite 1-1 was 0.7 Ω·cm.

Example B3-2

The relationship between density and volume resistivity was examined byexactly the same method as the method described in Example B3-1, exceptthat Composite 1-1 obtained in Example B1-2 was used. FIG. 21 shows themeasurement results. For example, when the density is 0.58 g/cc, thevolume resistivity of Composite 1-2 was 0.05 Ω·cm.

Comparative Example B2-1

The relationship between density and volume resistivity was examined byexactly the same method as the method described in Example B3-1, exceptthat the ultrafine fibrous carbons obtained in Comparative Example B1-1was used. FIG. 21 shows the measurement results. For example, when thedensity is 0.58 g/cc, the volume resistivity of the ultrafine fibrouscarbons (CNF) was 0.05 Ω·cm.

Comparative Example B2-2

The relationship between density and volume resistivity was examined byexactly the same method as the method described in Example B3-1, exceptthat acetylene black prepared in Comparative Example B1-2 was used. FIG.21 shows the measurement results. FIG. 21 shows the measurement results.For example, when the density is 0.58 g/cc, the volume resistivity ofacetylene black was 0.12 Ω·cm.

Relationship between Density and Volume Resistivity>

Referring to FIG. 21, the volume resistivity of Composite 1-1 obtainedin Example B1-1 showed a higher resistivity than the volume resistivityof acetylene black prepared in Comparative Example B1-2 but was at apractically problem-free level. The volume resistivity of Composite 1-2obtained in Example B1-2 was substantially identical to or better thanthe volume resistivity of the ultrafine fibrous carbons obtained inComparative Example B1-1 and showed a lower resistivity than the volumeresistivity of acetylene black prepared in Comparative Example B1-2.From these, it can be understood that Composite 1-1 and Composite 1-2have excellent electrical conductivity while maintaining excellentmechanical strength attributable to the ultrafine fibrous carbons(reinforcement effect).

Example B3-2

Evaluation of discharge rate characteristics was performed usingComposite 1-2 obtained in Example B1-2.

Production of Positive Electrode>

A slurry was manufactured by using 2 parts by mass of Composite 1-2 asan electroconductive agent, 91 parts by mass of carbon-coated LiFePO₄(SLFP-ESO1, produced by Hohsen Corp.) as a positive electrode activematerial, 7 parts by mass of polyvinylidene fluoride as a binder, andN-methylpyrrolidone as a solution. The manufactured slurry was coated onan aluminum foil, dried and roll-pressed to manufacture a positiveelectrode. The electrode thickness was 35 μm, and the electrode densitywas 2.5 g/cm³.

Fabrication of Cell>

A half-cell for battery evaluation was fabricated by arranging thepositive electrode manufactured as above to face a metallic lithiumthrough a polyethylene porous separator and injecting an electrolyticsolution composed of an ethylene carbonate/ethyl methyl carbonate mixedsolution (3/7 by mass, produced by Kishida Chemical Co., Ltd.)containing LiPF₆ at a concentration of 1 mol/L, into a 2032 coin cell.

Evaluation of Discharge Rate Characteristics>

Using the cell fabricated as above, a charge/discharge test wasperformed by a charging/discharging device. The charge conditions were0.2 C constant-current charge until 4.0 V, then constant-voltage charge(0.01 C cut-off) and after a pause for 10 minutes, switchover todischarge. The discharge conditions were constant-current discharge ateach discharge rate by setting the lower limit voltage to 2.5 V. Thedischarge rate was stepwise increased in order of 0.2 C→0.5 C→1.0 C→2.0C→3.0 C→5.0 C.

FIG. 22 shows a chart of the discharge rate characteristics measured. Inaddition, the capacity maintenance ratio at a cut-off electrodepotential of 3 V (the 0.2 C discharge capacity is assumed to be 100%) isshown in Table B1 below.

Example B3-3

Evaluation of rate characteristics was performed in the same manner asin Example 3-2, except that Composite 1-3 obtained in Example B1-3 wasused as the electroconductive agent.

FIG. 23 shows a chart of the discharge rate characteristics measured. Inaddition, the capacity maintenance ratio at a cut-off electrodepotential of 3 V (the 0.2 C discharge capacity is assumed to be 100%) isshown in Table B1 below.

Comparative Example B3-1

Evaluation of rate characteristics was performed in the same manner asin Example 3-2, except that the ultrafine fibrous carbons (CNF) obtainedin Comparative Example B1-1 was used as the electroconductive agent.

FIG. 24 shows a chart of the discharge rate characteristics measured. Inaddition, the capacity maintenance ratio at a cut-off electrodepotential of 3 V (the 0.2 C discharge capacity is assumed to be 100%) isshown in Table B1 below.

Comparative Example B3-2

Evaluation of rate characteristics was performed in the same manner asin Example 3-2, except that acetylene black used in Comparative ExampleB1-2 was used as the electroconductive agent.

FIG. 25 shows a chart of the discharge rate characteristics measured. Inaddition, the capacity maintenance ratio at a cut-off electrodepotential of 3 V (the 0.2 C discharge capacity is assumed to be 100%) isshown in Table B1 below.

TABLE 3 Table B1: Capacity Maintenance Ratio at 3 V Cut-OffElectroconductive agent 0.5 C 1 C 2 C 3 C 5 C Example B3-2 CNF/AB (dryJM) 92% 83% 69% 58% 36% Example B3-3 CNF/AB (ball 89% 74% 56% 37% 0%mill) Comparative CNF 81% 53% 7% 0% 0% Example B3-1 Comparative AB 75%51% 1% 0% 0% Example B3-2

Third Aspect of the Present Invention>

The present invention is described more specifically below by referringto Examples, but the present invention is not limited thereto.

In Examples, the measurements of fiber diameter and fiber length of theultrafine fibrous carbons and the X-ray diffraction measurement ofultrafine fibrous carbons were performed according to the followingmethods.

The measurements of fiber diameter and fiber length of the ultrafinefibrous carbons and the X-ray diffraction measurement of ultrafinefibrous carbons were performed in the same manner as above.

Example C1 Production of Ultrafine Fibrous Carbons (Carbon-BasedElectroconductive Agent)

90 Parts by mass of high-density polyethylene (HI-ZEX (registeredtrademark) 5000SR, produced by Prime Polymer Co., Ltd.; melt viscosityat 350° C. and 600 s⁻¹: 14 Pa·s) as a thermoplastic resin and 10 partsby mass of synthetic mesophase pitch AR•MPH (produced by Mitsubishi GasChemical Company, Inc.) as a thermoplastic carbon precursor were meltkneaded by a same-direction twin-screw extruder (“TEM-26SS”,manufactured by Toshiba Machine Co., Ltd., barrel temperature: 310° C.,under nitrogen stream) to prepare a resin composition.

The resin composition above was spun from a spinneret at 390° C. by acylinder-type single-hole spinning machine to make a precursor moldedbody (a sea-island type composite fiber containing the thermoplasticcarbon precursor as an island component). The fiber diameter of theprecursor molded body was 300 μm. Subsequently, the precursor moldedbody was held at 215° C. for 3 hours in air by a hot-air drier to obtaina stabilized precursor molded body.

In a vacuum gas displacement furnace, the stabilized precursor moldedbody was then subjected to nitrogen purging, depressurization to 1 kPaand temperature elevation to 500° C. at a temperature rise rate of 5°C./min in the depressurized state and held at 500° C. for 1 hour toremove the thermoplastic resin and form a fibrous carbon precursor. Thefibrous carbon precursor was added to ion-exchanged water and pulverizedby means of a mixer for 2 minutes to disperse the fibrous carbonprecursor at a concentration of 0.1 mass %.

The dispersed fibrous carbon precursor was graphitized by elevating thetemperature from room temperature to 3,000° C. over 3 hours in an argongas atmosphere, then naturally cooled to room temperature, anddisintegrated by a dry jet mill apparatus (A-O Jet Mill, manufactured bySeishin Enterprise Co., Ltd.) to produce ultrafine fibrous carbons. Theaverage fiber diameter of the obtained ultrafine fibrous carbons was 300nm, the average fiber length was 16 μm, and a branching structure wasnot observed, in other words, a linear structure was confirmed. Inaddition, the average interplanar spacing d002 of (002) plane asmeasured by an X-ray diffraction method was 0.3375 nm. FIG. 27 shows ascanning electron micrograph (2,000 times magnification) of theultrafine fibrous carbons (CNF) produced.

<Manufacture of Slurry>

A slurry was manufactured by using 5 parts by mass of the ultrafinefibrous carbons (carbon-based electroconductive agent) produced asabove, 5 parts by mass of styrene butadiene rubber (SBR, produced byZeon Corporation) as a binder, 6 parts by mass of sodium carboxymethylcellulose (CMC-Na) having an etherification degree of 0.8 and a weightaverage molecular weight of 300,000 as a surfactant, and 500 parts bymass of ion-exchanged water as a solvent and mixing these by ultrasonicvibration.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed with an eye by usingthe slurry manufactured above. As for the evaluation method of waterdispersibility, the slurry was checked with an eye and when the slurrywas smooth and an agglomerate of ultrafine-fibrous-carbon aggregates wasnot present in the slurry, the water dispersibility of theultrafine-fibrous-carbon aggregates was judged as good. On the otherhand, when a visually confirmable agglomerate ofultrafine-fibrous-carbon aggregates was present in the slurry, the waterdispersibility of the ultrafine-fibrous-carbon aggregates was judged aspoor.

Manufacture of Electrode>

2 Parts by mass of the ultrafine fibrous carbons (carbon-basedelectroconductive agent) produced as above, 1.5 parts by mass of styrenebutadiene rubber (SBR, produced by Zeon Corporation) as a binder, 1.5parts by mass of sodium carboxymethyl cellulose (CMC-Na) having anetherification degree of 0.8 and a weight average molecular weight of300,000 as a surfactant, 95 parts by mass of graphite (NICABEADS, Type:P25B-XB, Nippon Carbon Co.) as a negative electrode active material, and100 parts by mass of ion-exchanged water were mixed to prepare anelectrode-forming slurry. The prepared electrode-forming slurry wascoated on a copper foil by a doctor blade, and the coatedelectrode-forming slurry was dried in a hot-air drier at 105° C. tomanufacture an electrode sheet.

Evaluation of Dispersibility in Electrode>

The surface of the electrode sheet manufactured above was observed by ascanning electron microscope, and the presence or absence ofagglomeration of the ultrafine fibrous carbons was checked. When anagglomerate was present, the dispersibility in the electrode was judgedas poor.

Example C2 Production of Ultrafine Fibrous Carbons (Carbon-BasedElectroconductive Agent)>

Ultrafine fibrous carbons having an average fiber length of 5 μm wasobtained by producing ultrafine fibrous carbons (carbon-basedelectroconductive agent) by exactly the same method as in Example C1,except that disintegration was performed not by a dry jet mill apparatusbut by a wet pulverizer (Star Burst, manufactured by Sugino MachineLimited).

Manufacture of Slurry>

A slurry manufactured by exactly the same method as the method formanufacture of slurry described in Example C1 was obtained by using theultrafine fibrous carbons produced as above.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed in the same manner asin Example C1 by using the slurry manufactured above.

Example C3 Production of Ultrafine Fibrous Carbons (Carbon-BasedElectroconductive Agent)>

Ultrafine fibrous carbons having an average fiber length of 16 μm wasobtained by producing ultrafine fibrous carbons (carbon-basedelectroconductive agent) by exactly the same method as in Example C1,except that disintegration by a dry jet mill apparatus was notperformed.

Manufacture of Slurry>

A slurry manufactured by exactly the same method as the method formanufacture of slurry described in Example C1 was obtained by using theultrafine fibrous carbons produced as above.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed in the same manner asin Example C1 by using the slurry manufactured above.

Comparative Example C1 Production of Ultrafine Fibrous Carbons(Carbon-Based Electroconductive Agent)>

Ultrafine fibrous carbons (carbon-based electroconductive agent) wasproduced by exactly the same method as in Example C1.

Manufacture of Slurry>

A slurry manufactured by exactly the same method as the method formanufacture of slurry described in Example

C1, except for not using 6 parts by mass of sodium carboxymethylcellulose (CMC-Na) having an etherification degree of 0.8 and a weightaverage molecular weight of 300,000 as a surfactant was obtained byusing the ultrafine fibrous carbons produced as above.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed in the same manner asin Example C1 by using the slurry manufactured above.

Example C4 Production of Ultrafine Fibrous Carbons (Carbon-BasedElectroconductive Agent)>

Ultrafine fibrous carbons (carbon-based electroconductive agent) wasproduced by exactly the same method as in Example C1.

Production of Surfactant-Modified Ultrafine-Fibrous-Carbon Fibers>

2 Parts by mass of the ultrafine fibrous carbons (carbon-basedelectroconductive agent) above was added to and dispersed in 500 partsby mass of N-methylpyrrolidone (best quality, produced by Wako PureChemical Industries, Ltd.) under stirring. To this dispersion liquid, asolution of 1.5 parts by mass of sodium carboxymethyl cellulose (CMC-Na)having an etherification degree of 0.8 and a weight average molecularweight of 300,000 dissolved in 500 parts by mass of ion-exchanged waterwas added to prepare a mixed solution. The resulting mixed solution washeated and concentrated to prepare a surfactant-modifiedultrafine-fibrous-carbon fibers.

Manufacture of Slurry>

A slurry was manufactured to have the same composition as the slurrydescribed in Example C1 by using the surfactant-modifiedultrafine-fibrous-carbon fibers produced as above.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed in the same manner asin Example C1 by using the slurry manufactured above.

Manufacture of Electrode>

A slurry was prepared to afford the same electrode composition as inExample C1 by using the surfactant-modified ultrafine-fibrous-carbonfibers produced as above, and an electrode was manufactured in the samemanner as in Example C1.

Evaluation of Dispersibility in Electrode>

The surface of the electrode sheet manufactured above was observed by ascanning electron microscope, and the presence or absence ofagglomeration of the ultrafine fibrous carbons was checked. When anagglomerate was present, the dispersibility in the electrode was judgedas poor.

Example C5 Production of Ultrafine Fibrous Carbons (Carbon-BasedElectroconductive Agent)>

Ultrafine fibrous carbons (carbon-based electroconductive agent) wasproduced by exactly the same method as in Example C1.

Production of Oxidatively-Treated Ultrafine-Fibrous-Carbon Fibers>

5 g of the ultrafine fibrous carbons (carbon-based electroconductiveagent) above was added to a mixed solution (mixed acid) of 50 ml ofconcentrated nitric acid (60 to 61%, special grade chemical, produced byWako Pure Chemical Industries, Ltd.) and 150 ml of concentrated sulfuricacid (95.0+%, special grade chemical, produced by Wako Pure ChemicalIndustries, Ltd.) under stirring. After mixing for 3 hours at roomtemperature, a solid material was collected by filtration, the solidmaterial was then washed with ion-exchanged water until the washingbecame neutral, and the solid material was dried to prepare anoxidatively-treated ultrafine fibrous carbon.

Evaluation of Graphite Structure of Oxidatively-Treated UltrafineFibrous Carbon>

The graphite structure of the oxidatively-treated ultrafine fibrouscarbons produced as above was evaluated by comparing the interplanarspacing d(002) of (002) plane and the crystallite size Lc(002) of thegraphite structure measured by powder X-ray diffraction, with d(002),i.e., 0.3372 nm, and Lc(002), i.e., 47.9 nm, of the ultrafine fibrouscarbons that was not oxidatively treated.

Evaluation of Residual Chemicals in Oxidatively-Treated UltrafineFibrous Carbon>

The oxidatively-treated ultrafine fibrous carbons produced as above wassubjected to temperature elevation from 25° C. to 500° C. at 10° C./minin a nitrogen atmosphere, and the mass decrease ratio at 25° C. relativeto the mass at 25° C. was measured, whereby the residual amount ofchemicals, etc. contained in the oxidatively-treated ultrafine fibrouscarbons was measured. If the mass decrease ratio is large, when used fora non-aqueous electrolyte secondary battery, reduction in the batterycapacity due to a side reaction is disadvantageously caused.

Manufacture of Slurry>

A slurry manufactured by exactly the same method as the method formanufacture of slurry described in Example C1 was obtained by using theoxidatively-treated ultrafine fibrous carbons produced as above.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed in the same manner asin Example C1 by using the slurry manufactured above.

Manufacture of Electrode>

A slurry was prepared to afford the same electrode composition as inExample C1 by using the oxidatively-treated ultrafine-fibrous-carbonfibers produced as above, and an electrode was manufactured in the samemanner as in Example C1.

<Evaluation of Dispersibility in Electrode>

The surface of the electrode sheet manufactured above was observed by ascanning electron microscope, and the presence or absence ofagglomeration of the ultrafine fibrous carbons was checked. When anagglomerate was present, the dispersibility in the electrode was judgedas poor.

Example C6 Production of Ultrafine Fibrous Carbons (Carbon-BasedElectroconductive Agent)>

Ultrafine fibrous carbons (carbon-based electroconductive agent) wasproduced by exactly the same method as in Example C1.

Production of Oxidatively-Treated Ultrafine-Fibrous-Carbon Fibers>

5 g of the ultrafine fibrous carbons (carbon-based electroconductiveagent) above was added to 200 ml of aqueous hydrogen peroxide (30.0 to35.5%, special grade chemical, produced by Wako Pure ChemicalIndustries, Ltd.) under stirring. After mixing for 3 hours at roomtemperature, a solid material was collected by filtration, and the solidmaterial was washed with ion-exchanged water and then dried to preparean oxidatively-treated ultrafine fibrous carbon.

Evaluation of Graphite Structure of Oxidatively-Treated UltrafineFibrous Carbon>

The graphite structure of the oxidatively-treated ultrafine fibrouscarbons produced as above was evaluated by comparing the interplanarspacing d(002) of (002) plane and the crystallite size Lc(002) of thegraphite structure measured by powder X-ray diffraction, with d(002),i.e., 0.3372 nm, and Lc(002), i.e., 47.9 nm, of the ultrafine fibrouscarbons that was not oxidatively treated.

Evaluation of Residual Chemicals in Oxidatively-Treated UltrafineFibrous Carbon>

The oxidatively-treated ultrafine fibrous carbons produced as above wassubjected to temperature elevation from 25° C. to 500° C. at 10° C./minin a nitrogen atmosphere, and the mass decrease ratio at 25° C. relativeto the mass at 25° C. was measured, whereby the residual amount ofchemicals, etc. contained in the oxidatively-treated ultrafine fibrouscarbons was measured. If the mass decrease ratio is large, when used fora non-aqueous electrolyte secondary battery, reduction in the batterycapacity due to a side reaction is disadvantageously caused.

Manufacture of Slurry>

A slurry manufactured by exactly the same method as the method formanufacture of slurry described in Example C1 was obtained by using theoxidatively-treated ultrafine fibrous carbons produced as above.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed in the same manner asin Example C1 by using the slurry manufactured above.

Manufacture of Electrode>

A slurry was prepared to afford the same electrode composition as inExample C1 by using the oxidatively-treated ultrafine fibrous carbonsproduced as above, and an electrode was manufactured in the same manneras in Example C1.

Evaluation of Dispersibility in Electrode>

The surface of the electrode sheet manufactured above was observed by ascanning electron microscope, and the presence or absence ofagglomeration of the ultrafine fibrous carbons was checked. When anagglomerate was present, the dispersibility in the electrode was judgedas poor.

[Evaluation Results and Discussion of Water Dispersibility]

FIG. 28 shows the results of evaluation of water dispersibility usingthe slurry manufactured in Example C1. As evident from FIG. 28, theslurry manufactured in Example C1 was formed as a smooth slurry, and thewater dispersibility of the ultrafine-fibrous-carbon aggregates wasgood. FIG. 29 shows the results of evaluation of water dispersibilityusing the slurry manufactured in Example C2. As evident from FIG. 29,the slurry manufactured in Example C2 was formed as a smooth slurry, andthe water dispersibility of the ultrafine-fibrous-carbon aggregates wasgood.

FIG. 30 shows the results of evaluation of water dispersibility usingthe slurry manufactured in Example C3. As shown in FIG. 30, a smallagglomerate of the ultrafine fibrous carbons was observed here and therein the slurry manufactured in Example C3. This agglomerate is consideredto be generated because since the production was not passed through adisintegration step, the ultrafine fibrous carbons were notdisintegrated and bundled ultrafine fibrous carbons were formed.

Incidentally, the water dispersibility of the ultrafine-fibrous-carbonaggregates in the slurry manufactured in Example C3 was not better thanthe water dispersibility of the ultrafine-fibrous-carbon aggregates inthe slurry manufactured in Examples C1 and C2, but the waterdispersibility of the ultrafine-fibrous-carbon aggregates in the slurrymanufactured in Example C3 was not at a poor level but at a practicallyproblem-free level.

FIG. 31 shows the results of evaluation of water dispersibility usingthe slurry manufactured in Comparative Example C1. As shown in FIG. 31,the ultrafine fibrous carbons in the slurry manufactured in ComparativeExample C1 were completely aggregated, and the water dispersibility ofthe ultrafine-fibrous-carbon aggregates was poor. This poor waterdispersibility is considered to be caused because since only asurfactant was mixed at the time of slurry preparation, the ultrafinefibrous carbons were not modified with a surfactant and hydrophobicityof the ultrafine fibrous carbons was maintained.

FIG. 32 shows the results of evaluation of water dispersibility usingthe slurry manufactured in Example C4. As evident from FIG. 32, theslurry manufactured in Example C4 was formed as a smooth slurry, and thewater dispersibility of the ultrafine-fibrous-carbon aggregates wasgood.

FIG. 33 shows the results of evaluation of water dispersibility usingthe slurry manufactured in Example C5. As evident from FIG. 33, theslurry manufactured in Example C5 was formed as a smooth slurry, and thewater dispersibility of the ultrafine-fibrous-carbon aggregates wasgood.

FIG. 34 shows the results of evaluation of water dispersibility usingthe slurry manufactured in Example C6. As evident from FIG. 34, theslurry manufactured in Example C6 was formed as a smooth slurry, and thewater dispersibility of the ultrafine-fibrous-carbon aggregates wasgood.

[Evaluation of Graphite Structure of Oxidatively-Treated UltrafineFibrous Carbon]

In the evaluation of the graphite structure of the oxidatively-treatedultrafine fibrous carbons manufactured in Example C5, the interplanarspacing d(002) was 0.3377 nm, and the crystallite size Lc(002) was 21.3nm, indicating that compared with the ultrafine fibrous carbons notsubjected to an oxidative treatment, the interplanar spacing wasincreased and the crystallite size was decreased. This change was at apractically problem-free level but was not preferred.

Likewise, in Example C6, d(002) was 0.3373 nm and Lc(002) was 47.7 nm.Compared with the ultrafine fibrous carbons not subjected to anoxidative treatment, the interplanar spacing was increased and thecrystallite size was decreased, but the change was small and absolutelynot a problem in practice.

[Evaluation of Residual Chemicals in Oxidatively-Treated UltrafineFibrous Carbon]

Relative to the mass decrease ratio of the ultrafine fibrous carbons notsubjected to an oxidative treatment, which was 0.6%, the mass decreaseratio in Example C6 was 1.3% and substantially not changed, whereas themass decrease ratio in Example C5 was 7.5% and large, and it wasconfirmed that in Example C5, when used for a non-aqueous electrolytesecondary battery, reduction in the battery capacity due to a sidereaction is disadvantageously caused.

[Evaluation of Dispersibility in Electrode]

FIG. 35 shows the results of evaluation of dispersibility in electrode,using the electrode manufactured in Example C1. As evident from FIG. 35,an agglomerate of ultrafine-fibrous-carbon aggregates was observed inthe electrode manufactured in Example C1, and it was confirmed that thedispersibility in electrode was insufficient. That is, thedispersibility was good in the evaluation results of waterdispersibility using a slurry, and the dispersibility may be good from amacroscopic perspective, but an agglomerate was formed from amicroscopic perspective and this is not good for the object of thepresent invention.

FIG. 36 shows the results of evaluation of dispersibility in electrode,using the electrode manufactured in Example C4. As evident from FIG. 36,the ultrafine-fibrous-carbon aggregates were dispersed in the electrodemanufactured in Example C4 and thus, the evaluation of dispersibility inelectrode was good.

FIG. 37 shows the results of evaluation of dispersibility in electrode,using the electrode manufactured in Example C5. As evident from FIG. 37,the ultrafine-fibrous-carbon aggregates were dispersed in the electrodemanufactured in Example C5 and thus, the evaluation of dispersibility inelectrode was good.

FIG. 38 shows the results of evaluation of dispersibility in electrode,using the electrode manufactured in Example C6. As evident from FIG. 38,the ultrafine-fibrous-carbon aggregates was dispersed in the electrodemanufactured in Example C6 and thus, the evaluation of dispersibility inelectrode was good.

TABLE 4 Table C1 Evaluative Judgment Evaluation Evaluation of Graphiteof Residual Structure of Chemicals in Oxidatively- Oxidatively-Treatment Method Evaluation of Water Treated Treated Dis- ModificationDispersibility Ultrafine Ultrafine Evaluation of integration Method withOxidative Slurry Fibrous Fibrous Dispersibility Method SurfactantTreatment Judgment Composition Carbon Carbon in Electrode Ex. dry jetmill mixing in — AA CMC + SBR — — A C1 electrode-forming solution Ex.wet grinding mixing in — AA CMC + SBR — — — C2 electrode-formingsolution Ex. none mixing in — A CMC + SBR — — — C3 electrode-formingsolution Comp. dry jet mill mixing in — C SBR — — — Ex.electrode-forming C1 solution Ex. dry jet mill modification in — AACMC + SBR — — AA C4 advance (CMC/NMP) Ex. dry jet mill mixing intreatment AA CMC + SBR A C AA C5 electrode-forming with solution mixedacid Ex. dry jet mill mixing in treatment AA CMC + SBR AA AA AA C6electrode-forming with H₂O₂ solution AA: Good, A: Fair, C: Bad

Fourth Aspect of the Present Invention>

The present invention is described more specifically below by referringto Examples, but the present invention is not limited thereto.

In Examples, the measurements of fiber diameter and fiber length of theultrafine fibrous carbons and the X-ray diffraction measurement ofultrafine fibrous carbons were performed according to the followingmethods.

The measurements of fiber diameter and fiber length of the ultrafinefibrous carbons and the X-ray diffraction measurement of ultrafinefibrous carbons were performed in the same manner as above.

Example D1 Production of Ultrafine Fibrous Carbon>

90 Parts by mass of high-density polyethylene (HI-ZEX (registeredtrademark) 5000SR, produced by Prime Polymer Co., Ltd.; melt viscosityat 350° C. and 600 s⁻¹: 14 Pa·s) as a thermoplastic resin and 10 partsby mass of synthetic mesophase pitch AR•MPH (produced by Mitsubishi GasChemical Company, Inc.) as a thermoplastic carbon precursor were meltkneaded by a same-direction twin-screw extruder (“TEM-26SS”,manufactured by Toshiba Machine Co., Ltd., barrel temperature: 310° C.,under nitrogen stream) to prepare a resin composition.

The resin composition above was spun from a spinneret at 390° C. by acylinder-type single-hole spinning machine to make a precursor moldedbody (a sea-island type composite fiber containing the thermoplasticcarbon precursor as an island component). The fiber diameter of theprecursor molded body was 300 μm. Subsequently, the precursor moldedbody was held at 215° C. for 3 hours in air by a hot-air drier to obtaina stabilized precursor molded body.

In a vacuum gas displacement furnace, the stabilized precursor moldedbody was then subjected to nitrogen purging, depressurization to 1 kPaand temperature elevation to 500° C. at a temperature rise rate of 5°C./min in the depressurized state and held at 500° C. for 1 hour toremove the thermoplastic resin and form a fibrous carbon precursor. Thefibrous carbon precursor was added to ion-exchanged water and pulverizedby means of a mixer for 2 minutes to disperse the fibrous carbonprecursor at a concentration of 0.1 mass %. This 0.1 mass % dispersionliquid was dried in a drier at 100° C. to produce ultrafine fibrouscarbons. The average fiber diameter of the obtained ultrafine fibrouscarbons was 300 nm, and a branching structure was not observed, in otherwords, a linear structure was confirmed. When the particle sizedistribution of the ultrafine fibrous carbons was measured by particlesize distribution measurement, the average fiber length was 20 μm. Inaddition, the average interplanar spacing d002 of (002) plane asmeasured by an X-ray diffraction method was 0.3375 nm. FIG. 40 shows ascanning electron micrograph (2,000 times magnification) of theultrafine fibrous carbons (CNF) produced.

Production of Ultrafine-Fibrous-Carbon Aggregates>

The ultrafine fibrous carbons produced above was continuously treatedfive times by an ultra-centrifugal mill (ZM100, manufactured by Retsch;rotor with 24 blades, pore size of screen: 0.08 mm, rotation speed:18,000 rpm), then graphitized by elevating the temperature from roomtemperature to 3,000° C. over 3 hours in an argon gas atmosphere, andnaturally cooled to room temperature, thereby aggregating a plurality ofultrafine fibrous carbons to produce ultrafine-fibrous-carbonaggregates.

Measurement of Fiber Length Distribution of Ultrafine-Fibrous-CarbonAggregates>

The volume-based fiber length distribution of theultrafine-fibrous-carbon aggregates was determined by measuring thevolume-based particle size distribution (%) of theultrafine-fibrous-carbon aggregates produced above by means of aparticle size distribution meter (Particle Image Analyzer, IF-200nano,manufactured by JASCO International Co., Ltd., solvent: ethanol, carbonfiber concentration: 0.05%).

Manufacture of Slurry>

A slurry was manufactured by using 5 parts by mass of the ultrafinefibrous carbons (carbon-based electroconductive agent) produced above, 5parts by mass of styrene butadiene rubber (SBR, produced by ZeonCorporation) as a binder, 6 parts by mass of sodium carboxymethylcellulose (CMC-Na) having an etherification degree of 0.8 and a weightaverage molecular weight of 300,000 as a surfactant, and 5 parts by massof ion-exchanged water as a solvent and mixing these by ultrasonicvibration.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed with an eye by usingthe slurry manufactured above. As for the evaluation method of waterdispersibility, the slurry was checked with an eye and when the slurrywas smooth and an agglomerate of ultrafine-fibrous-carbon aggregates wasnot present in the slurry, the water dispersibility of theultrafine-fibrous-carbon aggregates was judged as good. On the otherhand, when a visually confirmable agglomerate ofultrafine-fibrous-carbon aggregates was present in the slurry, the waterdispersibility of the ultrafine-fibrous-carbon aggregates was judged aspoor. The criteria for evaluation of water dispersibility were asfollows.

Criteria for Evaluation of Water Dispersibility

AA: Water dispersibility was very good.

A: Water dispersibility was good.

B: Water dispersibility was slightly poor.

C: Water dispersibility was poor.

CC: Water dispersibility was very poor.

Example D2 Production of Ultrafine Fibrous Carbon>

Ultrafine fibrous carbons was produced by exactly the same productionmethod as the production method described in Example D1.

Production of Ultrafine-Fibrous-Carbon Aggregates (Carbon-BasedElectroconductive Agent)>

Ultrafine-fibrous-carbon aggregates (carbon-based electroconductiveagent) was produced by exactly the same production method as theproduction method described in Example D1, except that the number oftreatments by an ultra-centrifugal mill was changed to 1.

Measurement of Fiber Length Distribution of Ultrafine-Fibrous-CarbonAggregates>

The fiber length distribution of the ultrafine-fibrous-carbon aggregatesproduced above was determined by exactly the same measurement method asthe measurement method described in Example D1.

Manufacture of Slurry>

A slurry was manufactured by exactly the same manufacturing method asthe method for manufacture of slurry described in Example D1 by usingthe ultrafine-fibrous-carbon aggregates produced above.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed by exactly the sameevaluation method as the evaluation method described in Example D1 byusing the slurry manufactured above.

Comparative Example D1 Production of Ultrafine Fibrous Carbon>

Ultrafine fibrous carbons was produced by exactly the same productionmethod as the production method described in Example D1.

Production of Ultrafine-Fibrous-Carbon Aggregates (Carbon-BasedElectroconductive Agent)>

Ultrafine-fibrous-carbon aggregates was produced by exactly the samemethod as the production method described in Example D1, except that theultrafine fibrous carbons produced above was not treated by anultra-centrifugal mill.

Measurement of Fiber Length Distribution of Ultrafine-Fibrous-CarbonAggregates>

The fiber length distribution of the ultrafine-fibrous-carbon aggregatesproduced above was determined by exactly the same measurement method asthe measurement method described in Example D1.

Manufacture of Slurry>

A slurry was manufactured by exactly the same manufacturing method asthe method for manufacture of slurry described in Example D1 by usingthe ultrafine-fibrous-carbon aggregates produced above.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed by exactly the sameevaluation method as the evaluation method described in Example D1 byusing the slurry manufactured above.

Comparative Example D2 Production of Ultrafine-Fibrous-Carbon Mixture>

Ultrafine fibrous carbons produced by exactly the same method as themethod described in Example D1 was pulverized by a wet pulverizer (StarBurst, manufactured by Sugino Machine Limited) to produce ultrafinefibrous carbons (S-CNF) having an average fiber length of 5 μm. Thisultrafine fibrous carbons (S-CNF) having an average fiber length of 5 μmand ultrafine fibrous carbons (CNF) produced by exactly the same methodas the method described in Example D1 were mixed in a mass ratio of 1:1to produce ultrafine-fibrous-carbon mixture.

Production of Ultrafine-Fibrous-Carbon Aggregates (Carbon-BasedElectroconductive Agent)

Ultrafine-fibrous-carbon aggregates were produced by aggregating aplurality of ultrafine-fibrous-carbon mixtures produced above.

Measurement of Fiber Length Distribution of Ultrafine-Fibrous-CarbonMixture>

The fiber length distribution of the ultrafine-fibrous-carbon mixtureproduced above was determined by exactly the same measurement method asthe measurement method described in Example D1.

Manufacture of Slurry>

A slurry was manufactured by exactly the same manufacturing method asthe method for manufacture of slurry described in Example D1 by usingthe ultrafine-fibrous-carbon aggregates produced above.

Evaluation of Water Dispersibility>

Evaluation of water dispersibility was performed by exactly the sameevaluation method as the evaluation method described in Example D1 byusing the slurry manufactured above.

[Results and Discussion of Fiber Length Distribution]

FIG. 41 shows the results of fiber length distribution of theultrafine-fibrous-carbon aggregates produced in Example D1. Referring toFIG. 41, two peaks of a first peak and a second peak were present in thefiber length distribution of the ultrafine-fibrous-carbon aggregatesproduced in Example D1. The ratio of the volume-based particle sizedistribution (%) of the first peak at a fiber length of 7 μm to thevolume-based particle size distribution (%) of the second peak at afiber length of 18 μm was 5, and thus, the number of ultrafine fibrouscarbons having a short fiber length was large (see, Table 1 below). Inaddition, the average value of fiber length of theultrafine-fibrous-carbon aggregates produced in Example D1 was 17 μm,and the median value was 15 μm (see, Table 2 below).

Here, the average value is a value obtained adding the values of fiberlength of all ultrafine fibrous carbons and dividing the resulting valueby the number of ultrafine fibrous carbons. The median value is a valueof fiber length, which lies right in the middle by number of ultrafinefibrous carbons when the ultrafine fibrous carbons are sorted from ashorter fiber length. In the case where the number of fiber lengths iseven, the median value is the average value of two fiber length valuesof ultrafine fibrous carbons near the middle. As the variation in thefiber length of the ultrafine fibrous carbons is larger, the averagevalue and the median value greatly differ and deviate from each other.

FIG. 42 shows the results of fiber length distribution of theultrafine-fibrous-carbon aggregates produced in Example D2. Referring toFIG. 42, two peaks of a first peak and a second peak were present in thefiber length distribution of the ultrafine-fibrous-carbon aggregatesproduced in Example D2. The ratio of the volume-based particle sizedistribution (%) of the first peak at a fiber length of 10 μm to thevolume-based particle size distribution (%) of the second peak at afiber length of 25 μm was 3. That is, the volume ratio (%) of a shortultrafine fibrous carbons having a fiber length of 15 μm or lesscontained in the ultrafine-fibrous-carbon aggregates produced in ExampleD2 was slightly smaller than the volume ratio (%) of a short ultrafinefibrous carbons having a fiber length of 15 μm or less contained in theultrafine-fibrous-carbon aggregates produced in Example D1 (see, Table 1below). In addition, the average value of fiber length of theultrafine-fibrous-carbon aggregates produced in Example D2 was 20 μm,and the median value was 17 μm (see, Table 2 below).

FIG. 43 shows the results of fiber length distribution of theultrafine-fibrous-carbon aggregates produced in Comparative Example D1.Referring to FIG. 43, one peak at a fiber length of 25 μm was present inthe fiber length distribution of the ultrafine-fibrous-carbon aggregatesproduced in Comparative Example D1 (see, Table 1 below). In addition,the average value of fiber length of the ultrafine-fibrous-carbonaggregates produced in Comparative Example D1 was 24 μm, and the medianvalue was 18 μm (see, Table 2 below).

FIG. 44 shows the results of fiber length distribution of theultrafine-fibrous-carbon aggregates produced in Comparative Example D2.Referring to FIG. 44, two peaks were present in the fiber lengthdistribution of the ultrafine-fibrous-carbon aggregates produced inComparative Example D2. The ratio of the volume-based particle sizedistribution (%) of the peak at a fiber length of 3 μm to thevolume-based particle size distribution (%) of the peak at a fiberlength of 25 μm was 1. That is, it could be confirmed that the volumeratios of these two peaks are identical and the fiber length has a widedistribution (see, Table 1 below). In addition, the average value offiber length of the ultrafine-fibrous-carbon aggregates produced inComparative Example D2 was 14 μm, and the median value was 12 μm (see,Table 2 below).

[Evaluation Results and Discussion of Water Dispersibility]

The result of evaluation of water dispersibility using the slurrymanufactured in Example D1 was, as shown in Table 1, rated very good andscored as AA. The slurry manufactured in Example D1 was formed as asmooth slurry, and thus, the water dispersibility of theultrafine-fibrous-carbon aggregates was very good.

The result of evaluation of water dispersibility using the slurrymanufactured in Example D2 was, as shown in Table 1, rated good andscored as A. An agglomerate of the ultrafine fibrous carbons wasobserved here and there in the slurry manufactured in Example D2. Thisis considered to occur because the volume ratio (%) of a long ultrafinefibrous carbons having a fiber length of more than 15 μm contained inthe ultrafine-fibrous-carbon aggregates produced in Example D2 isslightly larger than the volume ratio (%) of a long ultrafine fibrouscarbons having a fiber length of more than 15 μm contained in theultrafine-fibrous-carbon aggregates produced in Example D1, andtherefore an agglomerate of the ultrafine fibrous carbons is more likelyto be formed in the ultrafine-fibrous-carbon aggregates produced inExample D2 than in the ultrafine-fibrous-carbon aggregates produced inExample D1. However, the slurry manufactured in Example D2 was formed asa relatively smooth slurry, and thus, the water dispersibility of theultrafine-fibrous-carbon aggregates was good.

The result of evaluation of water dispersibility using the slurrymanufactured in Comparative Example D1 was, as shown in Table 1, ratedslightly poor and scored as B. In the slurry manufactured in ComparativeExample D1, an agglomerate of the ultrafine fibrous carbons wasobserved. This is considered to occur because a bundled ultrafinefibrous carbons is formed due to a long ultrafine fibrous carbons havinga fiber length of more than 15 μm contained in theultrafine-fibrous-carbon aggregates produced in Comparative Example D1.

The result of evaluation of water dispersibility using the slurrymanufactured in Comparative Example D2 was, as shown in Table 1, ratedpoor and scored as C. In the slurry manufactured in Comparative ExampleD2, an agglomerate of the ultrafine fibrous carbons was observed. Thisis considered to occur because since the volume ratio (%) of a longultrafine fibrous carbons having a fiber length of more than 15 μmcontained in the ultrafine-fibrous-carbon aggregates produced inComparative Example D2 was 50 vol % or more relative to the volume ratio(%) of the entire ultrafine-fibrous-carbon aggregates, a bundledultrafine fibrous carbons was formed.

TABLE 5 Table D1 Volume-based Particle Size Distribution (%) Fiber ofFirst Length Fiber Peak/Volume-based of First Length of Particle SizePeak Second Distribution (%) Water (μm) Peak (μm) of Second PeakDispersibility Example D1 7 18 5 AA Example D2 10 25 3 A Comparative 25— B Example D1 Comparative 3 18 1 C Example D2

TABLE 6 Table D2 Average Value of Median Value of Standard Fiber Length(μm) Fiber Length (μm) Deviation Example D1 17 15 7 Example D2 20 17 11Comparative 24 18 20 Example D1 Comparative 14 12 7 Example D2

1. An electrode active material layer comprising at least an electrodeactive material, a carbon-based electroconductive agent and a binder,wherein said carbon-based electroconductive agent contains ultrafinefibrous carbons having a linear structure and an average fiber diameterof more than 200 nm to 900 nm, and wherein the in-plane maximum tensilestrength σ_(M) of said electrode active material layer and the in-planetensile strength σ_(T) in the direction perpendicular to the directionof said maximum tensile strength σ_(M) satisfy the followingrelationship (a):σ_(M)/σ_(T)≦1.6  (a)
 2. The electrode active material layer according toclaim 1, wherein said electrode active material layer comprises saidcarbon-based electroconductive agent in an amount of 10 mass % or less,based on the total mass of said electrode active material layer.
 3. Theelectrode active material layer according to claim 1, wherein saidelectrode active material layer comprises the binder in an amount of 1to 25 mass %, based on the total mass of said electrode active materiallayer.
 4. The electrode active material layer according to claim 1,wherein the average fiber length of said ultrafine fibrous carbons isfrom 1 to 15 μm.
 5. The electrode active material layer according toclaim 1, wherein said ultrafine fibrous carbons contain ultrafinefibrous carbons having an average fiber length of 1 to 15 μm andultrafine fibrous carbons having an average fiber length of more than 15μm to 50 μm.
 6. A non-aqueous electrolyte secondary battery comprisingthe electrode active material layer according to claim
 1. 7. Acarbon-based electroconductive agent, wherein said carbon-basedelectroconductive agent comprises ultrafine fibrous carbons having alinear structure and an average fiber diameter of more than 200 nm to900 nm, and wherein the average fiber length of said ultrafine fibrouscarbons is from 1 to 15 μm.
 8. A carbon-based electroconductive agent,wherein said carbon-based electroconductive agent comprises ultrafinefibrous carbons having a linear structure and an average fiber diameterof more than 200 nm to 900 nm, and wherein said ultrafine fibrouscarbons contain ultrafine fibrous carbons having an average fiber lengthof 1 to 15 μm and ultrafine fibrous carbons having an average fiberlength of more than 15 μm to 50 μm.
 9. The electrode active materiallayer according to claim 1, wherein said electrode active material layercomprises a composite, where said ultrafine fibrous carbons andspherical carbon are integrally attached to each other and uniformlymixed with each other. 10-18. (canceled)
 19. A non-aqueous electrolytesecondary battery comprising the electrode active material layeraccording to claim
 9. 20-29. (canceled)
 30. Ultrafine-fibrous-carbonaggregates, comprising aggregated ultrafine fibrous carbons having alinear structure, wherein at least a part of the surface of saidultrafine fibrous carbons in at least a part of saidultrafine-fibrous-carbon aggregates is modified with a surfactant,and/or at least a part of the surface of the ultrafine fibrous carbonsin at least a part of said ultrafine-fibrous-carbon aggregates isoxidatively treated, and wherein, in the volume-based fiber lengthdistribution of said ultrafine-fibrous-carbon aggregates, which isobtained by measuring the volume-based particle size distribution, afirst peak exists at a fiber length of 15 μm or less and a second peakexists at a fiber length of more than 15 and the ratio of thevolume-based particle size distribution (%) of said first peak to thevolume-based particle size distribution (%) of said second peak is 3/1or more.
 31. The ultrafine-fibrous-carbon aggregates according to claim30, wherein the average fiber length of said ultrafine fibrous carbonsin said ultrafine-fibrous-carbon aggregates is 25 μm or less.
 32. Theultrafine-fibrous-carbon aggregates according to claim 30, which isformed through a treatment in an ultra-centrifugal mill.
 33. Theultrafine-fibrous-carbon aggregates according to claim 30, wherein theaspect ratio of said ultrafine fibrous carbons in saidultrafine-fibrous-carbon aggregates is from 1 to 1,000.
 34. Acarbon-based electroconductive agent comprising theultrafine-fibrous-carbon aggregates according to claim
 30. 35. Anelectrode material for a non-aqueous electrolyte secondary battery,comprising at least the carbon-based electroconductive agent accordingto claim 34, an electrode active material, and a binder.
 36. Theelectrode material for a non-aqueous electrolyte secondary batteryaccording to claim 35, which further contains water as a solvent.
 37. Anelectrode for a non-aqueous electrolyte secondary battery, comprising acollector and an active material layer on said collector, wherein saidactive material layer is composed of the electrode material for anon-aqueous electrolyte secondary battery according to claim
 35. 38. Anon-aqueous electrolyte secondary battery comprising the electrode for anon-aqueous electrolyte secondary battery according to claim 37.